Hello.

I'd like to get opinions, suggestions for a toilet venting design in a tight space.

I imagine using a Wye (4 inch) lying flat to combine two waste lines (one is the toilet flange), then have a 2" vent immediately after the Wye, at 45 deg upright turn. I'm attaching a drawing.

I read on other posts that a flat Wye works for non-venting purposes. Will this work; is it correct to do?



The long, gory description:

The area in question is the transition from floor 1 (toilet, sink, shower) to cellar. Waste pipes bend 90 degrees and run across the cellar ceiling in-between joists; I don't want to run below joists or modify joists. The space is tight, enough for two 4" and one 2" no-hub pipes next to each other. I'd like to stick to 4" waste pipes.

One 4" waste pipe is for floor 1 sink, and floor 2 bathroom.
Second 4" waste pipe is for floor 1 toilet flange, immediately above cellar.

I imagine a 2" vent for the floor 1 toilet and would like to know whether the design is correct:
* Placement downstream from flange, but after combination of two 4" waste pipes
* Use of a "Cast Iron Upright Wye" (product #221656) for the 4" combination, but lying flat, which helps me with the "tight space" (the two parallel 4" fittings are close together, for a total width of 9-1/8 inch).
* 45-degree up-turn for 2" vent to avoid back-flow and clog
* I read that a horizontal vent is incorrect because it can cause backflow into the vent, hence the 45 degree turn. Does this argument also hold for the "flat" junction of two 4" wet waste pipes? Or is the assumption here that fluids traveling down either pipe will always clear out any misdirected doo-doo, something air in vents cannot do.

I am attaching a drawing for context.

I appreciate your time!

you can not tie the upstairs fixtures into the vent stack above the first floor without individually venting the first floor.
you can take the top floor drain and bring it separetly down to the basement and tie it in below.

Hi. Thanks for your reply.

I see - I cannot use wet venting across floors.

I've separated out the vents per floor in the below diagram. Does that work?

Re. bringing down the waste pipe from floor 1 into the basement and tying it in there: is it really necessary to have a separate waste pipe from each floor and combining in the cellar? Is it not correct to have a single waste pipe for all floors? Perhaps I'm misunderstanding.

Thank you!

The lower toilet needs to be vented separate from the drainage stack. Can you tie the toilet vent into the shower vent?

Hi.

Thanks for your reply.

I can tie the toilet vent into the shower vent above the cellar ceiling.

The way I understand your comment: the bottom toilet's vent must come before, not after, the combination of waste pipes.

I've updated the diagram. Nevermind the awkward criss-cross - that can be better arranged in the field.

Thoughts? Is the flat-placed Wye correct to combine two waste pipes? Is the design in good shape now?

Thank you.

Correct on the toilet vent and all the vent piping should not be required be larger than 2 in unless you have a local requirement for 3-in going through the roof for frost closure. The vent for the shower only needs to be 1 1/2".

Splendid!

Thank you Steve and thank you Packy. I appreciate your fast and straightforward responses.

You can simplify by wet venting the toilet with the sink. Also, a 3" drain pipe is sufficient for 2 bathrooms.

Ah, great! That does help. Thank you!



Edited 1 times.