Plumbing? I could've swore 24th century+ toilets have matter dematerializers that break down all waste products into their basic elements for re-use in the matter tanks.
=D
Pretty much. I just assume the toilet removes the material under the floor, where it is stored for a period of time until a transport cycle removes it into a bulk matter storage tank, and it is recycled with the rest of the bulk matter via replicators as food or other material via the Replimat.
In earlier eras, the material was broken down and removed by robots, who, of course, placed it in cargo containers for use by the protein resequencers.