The flowing back of used, contaminated, or polluted water from a plumbing fixture or vessel into the pipe which feeds

The placing of timbers, usually set in a diagonal or oblique position, to hold a wall in place.

Pressure developed in opposition to the flow of liquid or gas in a pipe, duct, conduit, etc.; due to friction,

1. A threaded nut, one side of which is dished to retain a grommet; used in forming a watertight pipe