: a quick question on a toilet drain.i am adding an addition to my house with a bathroom. the drain for this bathroom will be piped to the existing septic pipe on a seperate run. the bathroom is below grade ,so we installed a zoller ejector pump and basin into the floor that will be poured soon.my question is the drain leading into the basin under the cement floor to the toilet,(do we need a trap) in this drain pipe?the pluming supply house said we do not need it just an elbow, and the toilet acts as the trap.