Bathroom traps. Home › Forums › Public Forums › Drainage & Sewerage › Bathroom traps. This topic contains 0 replies, has 1 voice, and was last updated by firstname.lastname@example.org 6 years, 7 months ago. Author Posts 28 Mar 2013 at 1:35 pm #280116 email@example.com I need to reduce the depth of plumbing fittings under my bathroom floor, so that a new room can be built underneath. For floor waste, a bath drain, and a basin drain, can the piping be 40mm if connected directly to a 100mm main ?Can the traps for these be made less than 130mm in total height ? Many thanks. Author Posts You must be logged in to reply to this topic.