toilet rough in

Discussion in 'Toilet Forum discussions' started by Andrew M, Apr 15, 2007.

  1. Andrew M

    Andrew M New Member

    Feb 17, 2007
    I am a newbi so bear with me. 2 questions. I am building a new bath from scratch. What size hole do I need in the floor for the toilet ABS ? Second question is more difficult. I have hear people talk about the risk of "Siphon effect" if my vent pipes are not installed exactly correct. Can someone expand on this?
  2. jimbo

    jimbo Plumber

    Aug 31, 2004
    San Diego
    The purpose of the vent on each plumbing fixture is so that a local vacuum does not develop, which would siphon the water out of the trap. The trap is to keep sewer gas out of the house.
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  4. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Sep 2, 2004
    Retired Systems engineer for defense industry.
    New England
    The size hole to leave for a toilet drain is a little subjective. Depends on the type of flange you use and the height of the finished floor and the size of the drain line (3" minimum, 4" typically max). If you use a 4" line, you can butt the flooring up to it directly, since you can buy a flange that will fit inside of the 4" pipe. If you go with 3", then you need enough room outside of the pipe for the taperd part and the thickness of the flange. So, it's hard to give an exact amount.
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