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

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.