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Bathroom Drainage Layout for Connecting Drains in Bathroom Install

Postby Ross Logan » Sat Feb 16, 2019 7:46 am

Hi there
I’m installing a new bathroom (with neighbouring separate toilet room) on the first floor, and would like some help to know the best way to connect the drains together.
The toilet drain will run in the joist space (approx. 17cm high) horizontally approx. 1.5m, then bend vertically to run 3m down to the lower floor (there is no vent on this vertical section). There are two other drains to connect in to this somewhere:
(a) A small sink in the toilet, vented through the roof. This is able to meet the toilet drain within the joist space.
(b) A bathroom handbasin (vented to the roof), running to a shower which will be on a slightly raised floor, so that the drain can run across the top of the joists. This drain will have to cross the top of a joist before descending to meet the toilet drain.
I can see two possibilities:
1. The small sink drain runs horizontally, with the shower drain joining it with a Y, before running into the back (upstream) side of the toilet drain. Is there an appropriate fitting for this, ie a closet bend with a smaller (50mm) upstream connection? If so, this is certainly simpler.
2. The small sink drain and shower drain join together first with a Y, then run past the closet bend and join the toilet drain with a Y downstream of the toilet. Presumably this Y will need to be angled up slightly – what’s the minimum angle? How far downstream should this Y be?

I’d really appreciate advice on whether either or both of these options would work, and any other recommendations.
Ross Logan
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