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sideways from toilet into sewer? and 122mm pipe?

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  1. #1
    Apprentice (new member)
    Join Date
    Oct 2010

    Default sideways from toilet into sewer? and 122mm pipe?

    Hi All, I just found this forum and it looks great. Hopefully I'll be able to contribute as much as I've already gotten from this website, especially from wonderplumb's posts.

    My house is on a hill and has a large garage underneath that's half the size of the house and I never put my car in it. It's fitted-out well enough for blokes and my brothers stay down there when they visit so I'd like to put in an en-suite. Also the local Greensborough charities need more crisis housing so thought I'd do my bit.

    I'm doing as much pre-work as i can such as digging so the plumber is cheaper and can quote easier.

    I've done some digging and the toilet P trap exit would be just a bit higher than the sewer pipe that runs in the ground about 1m from the outside wall. The boundary gully is about 7m further downhill (at corner of house) and just above the level of the garage floor.

    Q1 - is this doable?
    Q2 - How does a 50mm pipe from a sink join in the 100mm pipe? given all the pipe are near horizontal and no riser.
    Q3 - my sewer pipe is 112mm as best i can measure (4.5inch I guess). Will this be a problem.
    Q4 - the toilet pipe exiting the external wall will be 300mm below ground level - is this allowed? With inspection tee?
    Q5 - what size hole saw should I get for 100m pipe? The plumbers that did my heater just smashed a hole through the bricks and filled the gaps with silicon, looks crap, is crap, don't want it to happen again.
    Q6 - is the height above the gully measured to the water level of the P trap, or to the height of the shower plug hole. Millimeters could make the difference meeting regs in this case.

    There is the possible option of coming out of the wall, turning 90 degree down, riser, 90 degrees back to near horizontal, continue downhill (underground) and meeting sewer pipe (which has a steeper incline) about 4m further along.

    Sorry about all the questions, it is for a good cause though.


  2. #2
    1K Club Member
    Join Date
    Jul 2007


    Hi David,

    Boundary gully. Do you mean overflow releif gully or boundary trap (where your sewer meets the main) ?

    A1) Yes, it sounds doable.
    A2) These two pipes of different diameters are connected using a fitting called a L.I.T. (level invert taper) which, by definition is now wrong as these must be installed with the top of the two pipes level meaning that they actually should be called a L.S.T. (level soffit taper).
    A3)The 112mm measurement is the outside diameter of standard 4" sewer pipe and shouldn't pose a problem.
    A4) Yes this can be done with an inspection opening (I.O.) immediately as it leaves the building.
    A5) You want a 125mm core hole for sewer pipe, the extra 10 or so mm allows the socket end of a fitting to fit in the hole.
    A6) Top of O.R.G. (overflow relief gully) must be at least 150mm below the spill level of the lowest fixture and 75mm above the surrounding ground so you really need the ground level outside to be 225mm below the floorwaste and/or shower grate. Otherwise you will need to have a reflux valve installed.
    Plumbers were around long before Jesus was a carpenter

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