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Thread: reducing toilet drain

  1. #1

    Default Code question: reducing in the toilet drain

    I am replumbing my 1st floor bath and have lots of headroom (altitude) in my basement ceiling below. Because of my need to come off the top of the trap arm in the basement with a 2 inch vent, I think that I need the piping to drop down below the floor joists before making the turn (to accomodate the vent take off). So I plan on dropping out of the closet flange straight by about 14 inches before going through the 90 and toward the drain.

    My question is: Is it ok to use a 4 inch closet flange > a 14 inch straight length of 4" ABS > a closet bend (4x3 spigot-hub REDUCING ) and then continue with the vent and sloping horizontal run in 3" ABS. The existing hole in my bathroom floor fits a 4 inch flange very easily - and a 3 inch flange would be loose. But running the entire drain in 4inch ABS for a powder room toilet is what I'd rather avoid.

    I know that code prohibits the reduction of pipe size in the direction of the flow but that there is an exception in the major codes for 4in by 3in closet bend fitting. Do you have to use the 4X3 closet bend fitting specifically ATTACHED to the closet flange or is an intermediate straight length of pipe there ok?

    Option B is to use a 3 inch flange (even though it feels sloppy in the hole) and then 14 inches of 3" into a 3 inch LS 90. This doesn't seem to be too bad but isn't a 4inch flange a better thing?

    Last edited by bingo; 02-16-2006 at 08:40 PM.

  2. #2
    Moderator & Master Plumber hj's Avatar
    Join Date
    Aug 2004
    Cave Creek, Arizona

    Default bend

    Here we would use a 4" x 3" reducing ell, also called a hub closet bend with a 4" riser. I just installed one yesterday, in fact, for a similar situation.


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