Bathroom drainage layout

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Ross Logan

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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/4.5" high) horizontally approx. 1.5m/4.5 feet, then bend vertically to run 3m/10 feet 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/2") 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.
Thanks.
 

frodo

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can you give a drawing of what you are proposing?
a picture of the area would be fantastically helpful

a wye hs to be turned up just enough so that the inlet is above the water line
typically you would twist the wye on a 22.5 or 45 degree angle to match your fittings

the vent must be back from the drain, 3 pipe diameters of the drain
9'' if it is a 3'' pipe
 

Ross Logan

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Thanks Frodo. I've attached a drawing of the layout and what I think the options are.
Thanks.Bathroom drainage options.jpg
 

Ross Logan

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I'd rather not drill through the joists, and I can get the two other drains into the same joist space as the toilet drain without doing so (the small sink one along through a wall and then down; the shower one can travel across the top of the joists).
But I think what you're suggesting is that both other drains join the main toilet drain AFTER the toilet, is that right? You've shown them joining the toilet drain separately - is that better than the two joining together first before the combined one joins the toilet drain?
 

frodo

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vent connection needs to be ''washed'' by drain, if not, stuff could creep up into the vent opening, dry out
and cause a problem over time

the science of crap, it's a tasty subject

problem with running the drain on top of the joist, is you are not going to have fall
again, over time, hair, soap scum. will sit in the pipe, because the water can not wash it away
and cause a hump....this hump, will catch new stuff, making the hump a big hump
then..on a wednesday, ''hump day..lol'' it will clog off, and you will be on here asking me how to snake the drain

drilling the joist is no big deal
as long as you are not drillling out the top or bottom but the middle, you are structurally ok
 

phishfood

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4 1/2" tall joists? Are these joists wood, structural steel? I have never run across 4 1/2" tall wooden joists.
 
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