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