Section 890.620  Overflows

a)         Design.  When any fixture is provided with an overflow, the waste piping shall be so designed that the standing water in the fixtures cannot rise in the overflow when the stopper is closed or remain in the overflow when the fixture is emptied.

b)         Connection.  The overflow pipe from a fixture shall be connected on the house or inlet side of the fixture trap, except that overflows of flush tanks may discharge into the water closets or urinals served by them.  No overflow shall be connected to any other part of the drainage system.