This is a home owner special. Basement bathroom sink.
I am aware of the S-trap. My question is in regards to the vent connection below the trap. The horizontal line goes through the back of the cabinet and wall. On the other side of the wall the vent goes vertical straight up to the floor joists and then horizontal to the vent pipe.
The sink seemed to drain fine during the inspection however it is my understanding that air should be introduced above the trap for proper drainage.
Any expert verbiage or code ref. would be helpful.
S traps are not allowed because of the possibility that siphoning can empty the trap. For that reason the trap needs to be below the horizontal portion of the drain.
The condition pictured can be repaired by disassembling the vertical pipe and moving the tee for the horizontal up higher using couplings and maybe a new Tee.
The horizontal pipe needs to be vented. The vent should not be much more than 30" from the trap (this may be farther away depending on the diameter of the horizontal pipe, larger diameters allow for greater distance to the nearest vent).
