Wiring the 12V Water Pump Branch Circuit

As part of the electrical planning for my cargo trailer conversion, this video was a solid reference for
wiring a dedicated branch circuit for the 12V water pump. It walks through layout, protection, and clean routing.

Video:

How to Wire a Water Pump – Branch Circuits | Ep: 4/10

I’m using this as a reference for:

Branch circuit layout for the water pump
Fuse/breaker sizing and protection
Wire routing near plumbing and mechanical components

Great Reference Video for Plumbing

While planning the plumbing for my cargo trailer conversion, I found this video really helpful for understanding
how flexible RV plumbing should be laid out and supported. It lines up well with the direction I’m taking on my build.

Video:

RV flexible plumbing fixed CORRECTLY!

I’m using this as a reference for:

Support spacing for PEX and flexible lines
Clean routing to avoid kinks and stress points
Serviceability around pumps, filters, and valves

Hot Water Heater Bypass Valve — A Small Upgrade With Big Benefits

One of the smartest additions you can make to any RV or cargo‑conversion plumbing system is a
hot water heater bypass valve. I recently watched a great walkthrough on how these valves work,
and it reinforced why this little setup is worth including in any build—especially one designed
for year‑round use.

What a Bypass Valve Does

A bypass valve gives you full control over whether water flows into the hot water heater or
around it. That flexibility matters for two major reasons:

1. Winterization Made Easy

When it’s time to winterize, you don’t want gallons of antifreeze filling your hot water tank.
A bypass valve lets you isolate the heater so antifreeze only travels through the lines—not the tank—
saving time, money, and cleanup.

2. System Flexibility & Maintenance

If you ever need to service, replace, or temporarily disable your water heater, the bypass lets you
keep the rest of your plumbing system fully operational. Cold water continues flowing to your fixtures
while the heater stays offline.

How It Works

A typical bypass setup uses two shutoff valves and a short crossover line:

Valve A: Stops cold water from entering the heater
Valve B: Stops hot water from exiting the heater
Crossover Line: Connects cold to hot so the system stays pressurized and functional

Turn two valves, and the entire heater is isolated. Simple, clean, and reliable.

Why I’m Including It in My Build

My plumbing system is designed for serviceability and future upgrades, and the bypass valve fits
perfectly into that philosophy. It supports:

Easy winterization
Quick maintenance
Future heater swaps (gas or electric)
Cleaner plumbing architecture

It’s a small detail that pays off every single year.

Tank vs. Tankless RV Water Heaters

Tank vs. Tankless RV Water Heaters for a Cargo Trailer Conversion

Plumbing
Systems Planning
Hot Water

As I plan the plumbing and hot water strategy for my cargo trailer conversion, I’ve been digging into the
real-world differences between traditional tank-style RV water heaters and
tankless/on-demand units. A recent video, “Tank Vs Tankless RV Water Heaters”,
pulled together a lot of practical experience from RV owners, and this post captures the key points
and how they apply to my build.

1. Hot Water Delivery and User Experience

Tank-style heaters store and pre-heat a fixed volume of water, so hot water is available
almost immediately at the faucet. You open the tap, and you’re essentially drawing from a pre-heated reservoir.

Tankless heaters work differently: they need a minimum flow to trigger the burner, then ramp up
to temperature. That means a delay before hot water arrives, and some variability as the system stabilizes.
Certain premium models (like the Truma AquaGo) offer a “comfort” or recirculation mode to keep water warm
in the lines, but that comes with additional energy use.

2. Water Usage and Conservation

One of the big tradeoffs with tankless systems is water waste during warm-up. Until the heater
reaches the target temperature and pushes that hot water all the way to the fixture, you’re sending usable water
down the drain. For anyone with limited gray tank capacity, that’s not trivial.

With a tank heater, the water is already hot and more predictable, so it’s easier to mix hot and
cold at the faucet and get to a comfortable temperature quickly. That can translate into less fiddling and less
waste overall.

3. Fuel, Power, and Flexibility

A common selling point for tankless heaters is efficiency: they only fire when water is flowing.
Many RV owners report lower propane usage after switching to tankless, especially if they take longer showers.

Tank heaters, on the other hand, often support multiple modes—propane, electric, or both.
That flexibility matters at campgrounds where shore power is available: you can save propane by running on
electric, or use both for faster recovery when demand is high.

4. Winter Performance and Cold-Weather Behavior

Cold weather exposes some of the weaknesses of tankless systems. They can be more sensitive to:

Low incoming water temperatures
Low water pressure or marginal pumps
Temperature rise limits across the heat exchanger

Owners in colder climates sometimes add insulation, small heaters, or circulation loops to keep lines from
freezing and to stabilize performance. By contrast, tank heaters tend to be more predictable
in winter, as the entire tank is kept at temperature and the system is generally simpler.

5. Installation, Tuning, and Reliability

Tankless units are more “tunable” but also more finicky. They care about:

Water pressure: too low and they may not fire consistently.
Flow rate: fixtures with very low-flow aerators can cause cycling.
Temperature rise: large jumps from cold inlet to hot outlet push the unit harder.

Tank heaters are mechanically simpler and often more forgiving. While both types can be reliable
when installed correctly, the tank-style design has fewer variables to tune and fewer edge cases to manage.

6. Real-World Experiences from RV Owners

The comments and user experiences around this topic are split, but informative:

Pro-tankless: Full-timers love the “endless shower” experience and reduced propane usage.
Back-to-tank: Some owners reverted to tank heaters after frustration with cold-weather
performance or water waste.
Hybrid setups: Others run creative combinations—small under-sink electric heaters,
recirculation loops, or dual-mode tank heaters—to get the best of both worlds.

How This Informs My Trailer Build

For my cargo trailer conversion, the decision isn’t just “tank vs. tankless”—it’s about how the entire
hot water system interacts with gray tank capacity, winter use, and
fixture layout.

Endless hot water is appealing, but the delay and extra water down the drain are real
concerns with a finite gray tank.
Cold-weather reliability matters, especially if the trailer sees shoulder-season or
winter trips.
A hybrid approach—for example, a traditional tank heater combined with a small
point-of-use electric heater near the shower or sink—could minimize wait time and water waste.
Heater placement relative to fixtures will be critical. Shorter runs mean less delay,
less wasted water, and a better overall experience regardless of heater type.

I’m leaning toward a solution that prioritizes predictability, water conservation, and serviceability,
even if that means giving up the “infinite” hot water promise of a pure tankless setup.

Waste Water Drain Tips

Cargo Trailer Conversion – Waste Water Drain Tips (Reference)

This page documents helpful waste‑water plumbing tips from the video
“Cargo Trailer Conversion Waste Water Drain Tips. Uniseal. Waste Water Tanks. RV Sewer Adapters.”
by I Ride Tiny House Adventures. I’m saving these notes as a reference for my own plumbing system design.

1. Using Uniseals for Tank Penetrations

The video highlights how effective Uniseals are for creating watertight penetrations in plastic waste tanks.
They allow pipes to pass through the tank wall without needing threaded bulkheads, and they flex with tank movement.

Key points:

Use a —cheap ones can cut oversized holes and cause leaks.
Lubricate the pipe and seal to avoid tearing the rubber during installation.
Uniseals work well for both grey and black water tanks.

2. Preventing Leaks at Fittings

One commenter recommended applying a small amount of grease on the gasket before tightening fittings.
This helps the gasket compress smoothly instead of dragging and tearing.

This is especially useful when installing:

Threaded adapters
Tank outlet fittings
RV sewer connectors

3. RV Sewer Adapters & Drain Options

The video shows how to adapt from smaller drain lines (1.5″) up to standard RV sewer sizes (3″).
This is helpful when combining shower, sink, or sump‑pump outputs into a larger drain system.

Tips mentioned:

Offset fittings can help align pipes when tank ports aren’t perfectly positioned.
Some builders downsize to a garden hose adapter for slow but simple grey‑water draining.
Always use high‑quality PVC fittings to avoid cracking under vibration.

4. Waste Tank Selection & Installation Notes

Viewers in the comments mentioned using 36–55 gallon tanks and pairing them with shower sump pumps for interior plumbing.
This aligns with my own plan to keep all tanks inside the trailer for freeze protection.

General reminders:

Verify tank wall thickness before choosing Uniseal sizes.
Support tanks fully—don’t rely on fittings to carry weight.
Plan drain locations early to avoid conflicts with framing.

5. Safety & Practical Tips

Use flush‑cut zip‑tie cutters to avoid sharp edges that can cut your hands.
Keep spare fittings and caps for emergency repairs.
Label drain lines during installation for easier troubleshooting later.

Why This Video Is Useful for My Build

This video provides practical, real‑world examples of how to handle waste‑water plumbing in a cargo trailer conversion.
The tips on Uniseals, gasket sealing, and sewer adapters will directly influence how I design my grey‑water system, sump‑pump connections, and tank penetrations.

This page will serve as an ongoing reference as I finalize my plumbing layout.

Save a Drop P3 Water Flow Meter – Fresh Water Fill Monitoring

As part of planning the fresh water system for this cargo trailer conversion, I wanted a simple way to
monitor how much water is going into the tanks during fills.
A small inline flow meter on the hose is an easy, low‑tech way to track gallons used and avoid overfilling.

One product I’m considering for this purpose is:

Save a Drop P3 Blue Water Flow Meter – Measure Gallon Usage from an Outdoor Garden Hose

Product Overview

The Save a Drop P3 is a compact, inline water flow meter that attaches to a standard garden hose.
It measures the total volume of water passing through and displays usage in gallons, making it useful for
filling RV or trailer fresh water tanks, portable containers, or even just tracking water consumption.

Type: Inline water flow meter
Connection: Standard garden hose
Display: Digital readout of gallons used
Use Case: Monitoring tank fills and conserving water

Why This Is Useful for the Build

When filling fresh water tanks, it’s easy to lose track of how much water has gone in—especially when filling from
portable containers or non‑metered sources.
A small flow meter like this provides:

Overfill awareness: Know how many gallons have gone into the tank before it reaches capacity.
Repeatable fills: Easy to track partial fills (e.g., “add 10 gallons” instead of “fill until it overflows”).
Water usage insight: Helps understand how quickly water is consumed during trips.
Portable and flexible: Can be used on any hose, not permanently installed.

How It Fits Into the Fresh Water Workflow

In practice, this meter would be attached inline on the hose used to fill the fresh water tank(s).
Before starting a fill, the meter can be reset to zero, and the display will show the total gallons added during that session.

Attach meter between spigot and hose, or hose and tank fill.
Reset meter before each fill.
Monitor gallons as the tank fills to avoid overfilling.
Optionally log usage to better understand daily water consumption.

This page serves as a reference for a simple, portable tool that can make tank filling more controlled and predictable,
especially when working with multiple tanks or off‑grid water sources.

Updated Diagram – Urine Separator, Sink Drain, Sump Pump, and Gray Tank System

This diagram shows the updated plumbing layout for the bathroom: the composting toilet’s urine separator and the bathroom sink both drain into the sump pump box.
The sump pump then sends all liquids to the interior gray tank, with a check valve placed before the gray tank to prevent any backflow.
The toilet sits elevated above the sump pump by at least one foot, ensuring reliable gravity flow.

System Diagram (Top‑Down Flow)


                 ┌───────────────────────────────┐
                 │     COMPOSTING TOILET         │
                 │   (Urine Separator Outlet)    │
                 └──────────────┬────────────────┘
                                │
                                │  Gravity-fed Urine Line
                                ▼
                 ┌───────────────────────────────┐
                 │       BATHROOM SINK           │
                 │  (Drain Tied Into Urine Line) │
                 └──────────────┬────────────────┘
                                │
                                ▼
                 ┌───────────────────────────────┐
                 │   COMBINED DRAIN LINE (1")    │
                 │  Sink + Urine to Sump Pump    │
                 └──────────────┬────────────────┘
                                │
                                ▼
                 ┌───────────────────────────────┐
                 │     SUMP PUMP BOX (12V)       │
                 │  - Collects shower water      │
                 │  - Collects urine + sink      │
                 │  - Auto pump activation       │
                 └──────────────┬────────────────┘
                                │ Pressurized Output
                                ▼
                 ┌───────────────────────────────┐
                 │         CHECK VALVE           │
                 │  (Prevents backflow from tank)│
                 └──────────────┬────────────────┘
                                │
                                ▼
                 ┌───────────────────────────────┐
                 │       INTERIOR GRAY TANK      │
                 │  - Receives all pumped liquid │
                 └───────────────────────────────┘

Side‑View Height Relationship


   [Composting Toilet]
            │
            │  (Urine Line)
            ▼
   [Sink Drain Tie-In]
            │
            ▼
   (Combined Drain Line)
            │
            ▼
   [Raised Shower Platform]───────────────┐
            │                              │
            ▼                              │
      [Sump Pump Box]  <───────────────────┘
            │   (Pumps upward)
            ▼
      [Check Valve]
            │
            ▼
      [Interior Gray Tank]

This layout ensures the toilet and sink both drain by gravity into the sump pump, while the sump pump handles all elevation changes needed to reach the gray tank.

Why the Sink Tie‑In Helps

Tying the bathroom sink into the urine line provides several benefits:

Flushes the urine line with clean water every time the sink is used.
Prevents salt buildup or odor in the urine hose.
Adds enough liquid volume to reliably trigger the sump pump float switch.
Reduces plumbing complexity by combining two low‑flow drains into one line.

Why the Check Valve Belongs Before the Gray Tank

Placing the check valve on the pressurized discharge line (not the urine line) ensures:

No gray water can flow backward into the sump pump box.
No contamination risk for the toilet or sink drain lines.
The sump pump remains protected from tank pressure or sloshing.

This updated diagram reflects the final intended flow path for the bathroom plumbing system and will be used as part of the full interior‑only plumbing documentation.

Build Notes – Floor, Insulation, and Bathroom Plumbing

Build Notes & Lessons Learned – Floor, Insulation, and Bathroom Plumbing

As I continue refining the design for the cargo trailer conversion, I’m collecting important details that will influence how the trailer is ordered and how the interior systems are built.
These notes focus on floor structure, insulation planning, and bathroom plumbing considerations based on research and reference videos.

No Dovetail for a Level Interior Floor

For this build, a flat, level floor is essential. This means the trailer must be ordered with no dovetail.
A dovetail is the angled drop at the rear of many cargo trailers, designed for loading low vehicles.
While useful for ramps, it creates an uneven interior floor and complicates cabinetry, flooring, and bathroom layout.

Choosing a non-dovetail rear ensures:

A fully level floor from front to back
Simpler installation of flooring, insulation, and cabinetry
Better support for the raised shower platform and tank placement

Interior Doors Must Be Raised for Floor Insulation

If the trailer does not come factory-insulated, the interior floor will be built up with insulation and subfloor layers.
This adds approximately 1.5 inches of height to the finished floor.

To avoid clearance issues:

Interior doors (bathroom, bedroom, etc.) must be raised at least 1.5″ during installation.
Dealers should not install interior trim — trim should be left loose inside the trailer.

This prevents the door from dragging on the finished floor and allows trim to be installed after insulation and flooring are complete.

Backer Boards Before Insulation (Video Reference)

In this video (timestamp 2:15):

Cargo Trailer Conversion – Insulation Prep

The creator explains the purpose of installing backer boards before adding insulation.
These boards provide:

A solid mounting surface for walls and fixtures
Structural support for areas where screws cannot bite into foam
Better rigidity and long-term durability

This reinforces the plan to include backer boards in key areas before insulating the walls and ceiling.

Urine Separator Plumbing Into Sump Pump (Video Reference)

In this video (timestamp 27:50):

Cargo Trailer Bathroom Plumbing – Urine Separator & Sump Pump

The builder demonstrates how the urine separator line from a composting toilet can be routed into the same shower sump pump box that feeds the gray tank.
This setup includes:

A dedicated urine drain line entering the sump box
A check valve to prevent backflow from the gray tank
Automatic pumping of both shower water and urine into the gray tank

This is a useful reference for integrating the composting toilet’s liquid output into the interior gray tank system without needing a separate container.

Summary

These notes help shape several key decisions for the build:

Order the trailer without a dovetail for a level interior floor.
Ensure interior doors are raised 1.5″ if insulating the floor after delivery.
Use backer boards before insulation for structural support.
Consider routing the urine separator into the sump pump with a check valve.

These insights will be incorporated into the final layout and construction plan as the build progresses.

Raised Shower Drain System – Diagram & Flow Path

This diagram illustrates how the raised shower platform, low‑profile drain, 12V sump pump box, and interior gray tanks work together as a complete drainage system.
The goal of this design is to keep all tanks inside the trailer, avoid any under‑floor tank mounting, and ensure reliable drainage even when the gray tanks sit higher than the shower pan.

System Overview Diagram

                 ┌───────────────────────────────┐
                 │       RAISED SHOWER PAN       │
                 │   (Built on framed platform)  │
                 └──────────────┬────────────────┘
                                │
                                ▼
                 ┌───────────────────────────────┐
                 │  LOW-PROFILE SHOWER DRAIN     │
                 │   (Scandvik 1" Outlet)        │
                 └──────────────┬────────────────┘
                                │ 1" Drain Line
                                ▼
                 ┌───────────────────────────────┐
                 │   12V SHOWER SUMP PUMP BOX    │
                 │   (Zuomeng 750 GPH)           │
                 │ - Collects shower water       │
                 │ - Auto pump activation        │
                 │ - 3/4", 1", 1-1/8" outlets    │
                 └──────────────┬────────────────┘
                                │ Pressurized Output
                                ▼
                 ┌───────────────────────────────┐
                 │     INTERIOR GRAY TANK(S)     │
                 │  (Mounted inside utility bay) │
                 │ - No exterior tanks            │
                 │ - Freeze-protected             │
                 └───────────────────────────────┘

Flow Path Explanation

The raised shower system works by elevating the shower pan enough to allow a drain line to flow into a compact sump pump box.
The sump pump then automatically transfers water into the interior gray tanks.

1. Raised Shower Platform: Provides vertical space for the drain and plumbing beneath the pan.
2. Low-Profile Drain: Minimizes height while allowing a 1″ outlet to feed the sump box.
3. Sump Pump Box: Collects water and pumps it upward or horizontally to the gray tanks.
4. Interior Gray Tanks: Store all wastewater inside the insulated trailer envelope.

Why This System Works for an Interior-Only Plumbing Layout

This configuration supports the goal of keeping all plumbing and tanks inside the trailer, avoiding exposure to road debris, freezing temperatures, and under‑frame clearance issues.

No exterior tanks: All tanks remain inside the conditioned space.
Freeze protection: Interior placement prevents winterization issues.
Flexible routing: Pumped discharge allows tanks to sit higher than the shower.
Compact footprint: Marine components are designed for tight spaces.

Component Placement Diagram (Top‑Down Layout)

 ┌─────────────────────────────── Trailer Bathroom ───────────────────────────────┐
 │                                                                                │
 │   [ Raised Shower ]                                                            │
 │        │                                                                        │
 │        ▼                                                                        │
 │   [ Low-Profile Drain ]                                                         │
 │        │                                                                        │
 │        ▼                                                                        │
 │   [ Sump Pump Box ]  →→→→→→→→→→→→→→→→→→→→→→  [ Interior Gray Tank(s) ]          │
 │                                                                                │
 └────────────────────────────────────────────────────────────────────────────────┘

Notes for Final Design

Confirm sump box placement for easy access to the lid and pump.
Plan for a service hatch or removable panel in the shower platform.
Use smooth‑bore hose for the pump discharge to reduce backpressure.
Ensure gray tank inlet height matches the sump pump’s lift capability.

This diagram will serve as a reference as the bathroom plumbing system is finalized and integrated into the overall trailer layout.

Shower Drain Components Under Consideration for the Bathroom Build

As I plan the raised shower platform for the bathroom, I am exploring different components that will allow the shower to drain directly into the interior gray tanks.
Keeping all tanks inside the trailer is a priority for freeze protection, maintenance access, and overall system reliability.
Two products that may play a role in this design are a low-profile shower drain and a compact 12V shower sump pump box.

Scandvik Low Profile Drain Stopper – 1″ Outlet

This drain is designed for marine environments where space is limited and drainage must be routed through tight areas.
Its low-profile design makes it a strong candidate for a raised shower floor where vertical clearance is limited.

Outlet Size: 1 inch
Design: Low-profile for tight installations
Intended Use: Marine showers and wet areas
Potential Benefit: Allows the shower pan to sit lower while still routing water into a sump box

This drain could be mounted directly into the raised shower platform, feeding into a sump pump box located beneath or adjacent to the shower structure.

Zuomeng 12V Automatic Shower Sump Pump Box – 750 GPH

This sump pump box is designed for boats and RVs to collect shower water and automatically pump it to a gray tank.
For a cargo trailer conversion with interior tanks, this type of system allows the shower to drain efficiently even when the gray tanks sit higher than the shower pan.

Brand: Zuomeng
Flow Rate: 750 GPH
Power: 12V DC (corded electric)
Material: ABS housing
Maximum Lifting Height: 10 feet
Item Weight: 4.64 lbs (2.11 kg)
Package Dimensions: 12.05″ × 10.55″ × 5.67″
Model Number: HY-056
Included Adapters: 3/4″, 1″, and 1-1/8″ hose fittings

The sump box collects water from the shower drain and automatically pumps it into the gray tanks, making it ideal for raised shower platforms or installations where gravity drainage is not possible.

How These Components Fit Into the Shower Design

The raised shower platform will allow the drain to sit above the sump box, which then pumps water into the interior gray tanks.
This approach eliminates the need for any tanks mounted under the trailer and keeps all plumbing inside the insulated envelope.

Low-profile drain: Minimizes height while providing a clean outlet into the sump box.
Sump pump box: Automatically moves water to the gray tanks regardless of tank height.
Interior-only plumbing: Improves freeze protection and simplifies maintenance.

These components are being documented here as part of the ongoing evaluation process for the bathroom plumbing system.
Final selections will be made once the shower platform height, tank placement, and plumbing layout are fully defined.