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.
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:
- Weep hole sends urine down the drain
- 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
- 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
- Flush without active pumping is used for urine
- Small or big flush can be used on a dual flush toiled
- 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 -  - or locally at Menards
- Spade terminals
- Hose Clamps