Separating Toilet

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A modern flush toilet that seperates urine from feces for use in applications (such as composting toilets, or biodigesters) where a urine-feces mix could lead to unbalances of chemicals. This innovation allows for the use of a regular flush toilet, and converting it to a separating toiled without any modification of the toilet - but only the plumbing below. This allows the use of a standard $100 toilet to achieve the separation function - instead of using a specialized $1000 separating toilet.

Used For

Industry Standards

Working Design Document

Note: we figured how to implement a urine separating function without modifying the flush toilet proper. Pages on toilet modification are for design study only, not for replication.


Diagram + Operation

Study this carefully to understand the points of logic:

  1. Weep hole sends urine down the drain
  2. Pressurized water at 50 PSI backflushes the weep hole via a washer solenoid - whenever feces are flushed so that the weep hole does not plug
  3. Feces are pumped actively via a macerating lift pump and enter the biodigester via 1" PVC pipe. Check valve after the pump prevents backwash from biodigester plumbing, where biodigester is loaded from the top
  4. Flush without active pumping is used for urine
  5. Small or big flush can be used on a dual flush toiled


Industry Standards

  • Separating toilets are common
  • No other biodigester-connected separating toiled for the temperate zone is known to the authors


  • 1/2" NPT to PEX valve - Supply House - [2] - or locally at Menards
  • Spade terminals
  • Hose Clamps