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Discuss DIYer - need help with toilet pipe air-valve install in the Plumbing Forum area at

  1. Riley

    Riley S. Mod Trusted Plumber GSR Top Contributor!!

    I’m also not being pedantic but I suspect your run from the shower to the drain is too long for 1.5”
    • Agree Agree x 1
  2. bogrodder

    bogrodder Plumber GSR

    The bath on emptying will pull the seal out of the shower. Each appliance should each have its own waste ideally to the stack and not all joined up.
    Last edited: Apr 17, 2019
  3. Coby kenny AGUILAR

    Coby kenny AGUILAR Member

    See if you can substitute the 3 x middle 90° for 2 x 45°'s

    If its already an internal stack take it high and fit a durgo if it's external take it past the highest outlet inside

    Not all outlets / sanitaryware need a vent, unless it's pulling a trap ect..

    If you want to play it safe fit anti-syphon trap under bath and basin there not that much dearer than a normal trap
  4. chris watkins

    chris watkins Plumber

    The 40mm waste pipe will pull any water filled traps on the all the fittings when the bath is drained Part H of the building regs sets out the maximum runs for single runs to single fittings once you start combining them then you need to increase the waste pipe size or add an anti-siphon pipe or mini AAAV or replace the water filled traps with waterless traps.
    The stack should be ventilated, the branch to the WC doesn't have to be but I would be tempted to run a 50mm anti picking up the WC & the bath (40 or even 32mm) if at all possible, run above overspill level of the pan & connected back into the dry part of the stack (vent pipe). In that way no mechanical devices would be required.
    Medium radius bends are fine so long as the float is installed with the correct falls (18 - 90mm per M) de-bur the pipes & you will not have any problems.
    • Like Like x 1
  5. pc__upf

    pc__upf New Member

    Thank you all for your replies - very helpful stuff.

    Ok, so install anti-syphon traps on shower/bath/basins.

    AAV or Durgo on 40mm pipe. Inside eaves ok? see diagram.

    AAV/Durgo not required for toilet, but better if it has it? Or definitely required? Or not needed at all?

    I'll attempt to use 2 x 45° bends instead of the first 90.


    Did I capture everything? Thanks again everyone.
  6. pc__upf

    pc__upf New Member

    @ChrisWatkins - many thanks, very helpful.

    Is this what you mean?

  7. chris watkins

    chris watkins Plumber

    No, you don't need & probably shouldn't have a "Durgo" on the main stack, can't terminate to atmosphere ? if it can then the loop is find but not essential it is more to try to anti the bath run so it will not self-syphon when discharged. Otherwise couldn't you run it separately along the eaves to connect directly to the stack?
    Remember this work is covered by Building Control & you should be talking to them.
    Please don't use anti-vac traps you may well live to regret it.
    Try this type of trap = Sanitary waste valve in bathroom applications
  8. pc__upf

    pc__upf New Member

  9. Riley

    Riley S. Mod Trusted Plumber GSR Top Contributor!!

    Are you running the shower waste through joists
  10. pc__upf

    pc__upf New Member

    It was like that when we bought the house.
  11. Coby kenny AGUILAR

    Coby kenny AGUILAR Member

    You've got the right idea now,

    Waterless traps are great but put them where they're accessible, anything compression should have access.

    The 'outside pipe' should tee up above the roof if you're unable to do this and have a boxing or void behind the pan / toilet, take it up as far as you can go or same height as the Cistern and put a durgo on it
    • Like Like x 1
  12. Riley

    Riley S. Mod Trusted Plumber GSR Top Contributor!!

    Doesn’t make it right though. Weakened joists and all that
  13. chris watkins

    chris watkins Plumber

    The bath connection is the main problem one for siphonage because of both the volume of water & how quickly it discharges. Not so with the shower because the water flow is much slower & there is normally water draining away slowly after the shower is off, this will refill a water trap even if the seal is lost.
    All waste connections to 110mm soil pipes should ideally be made either in a vertical section or on top of a horizontal (it is normally taken that only the bottom 2/3rd of the pipe will be wet) but you will need to take care if you are close to the back of the pan because the solids may not be fully broken up & there could be splashing as the water leaves the Pan.
    You may wish to put a small (40mm) AAAV (Durgo) on the basin run, put it up as high as you can under the counter on the 40mm tee & run 40mm float only reducing to 32mm as you come across to each basin trap.
  14. chris watkins

    chris watkins Plumber

    I am still concerned that you may not be venting the stack, can you get the vertical stack outside to vent correctly to atmosphere?
    Will this be the only vent on your drainage system?
    By Law the head of the run must be vented !!!
    • Winner Winner x 1
  15. pc__upf

    pc__upf New Member

    Chris, thanks so much for all this.

    This is not the main drainage system of the house. This is literally just this one bathroom, which was added by the previous owners.

    IMG_0349.jpg IMG_6A9DE11B843D-1.jpeg
    1) AAV added to 4 in pipe behind wall.
    2) Bath (with waterless trap) connects to toilet's 4 in behind wall with boss connector (see link below). May connect at exactly half line due to slope. Problem?
    3) Waterless trap on bath and one on each basin (or one shared)
    4) Normal trap under shower (no access)
    5) 40mm AAV on the way out of both basins (confirm location-diagram)

    Questions :
    1) For two basins, should I install one waterless trap on each, or can they share one after a tee? (the tee can be the AAV?)
    2) If using waterless traps, the syphoning may not be a problem any more. If joining bath waste to 4 in pipe too close to toilet is a concern, can the bath waste return to the original path and join the shower pipe?
    3) Don't know what a 40mm float is.

    Here's the shopping list so far : Please recommend alternatives if these are bad for any reason.

    110mm AAV (Durgo) :

    40mm AAV for basin:

    Boss Connector : Water Waste BIG BOSS Pipe Adaptor - 40mm - 1.1/2"- Black - Pipe & Fittings | |

    Waterless trap:
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