I have broken up the concrete in my basement for a new bathroom. There are drains that have been roughed in by the builder, but the layout won't work for us so I'm going to rearrange.

Hopefully the picture can give an idea of which way the drains are going. I've attached a picture showing the preferred locations for the toilet, sink, and shower.

Would the drain layout work? I added a vent in green for the shower, but unsure if it is needed. A few people I have talked to have said it is needed, and others have said with horizontal (wet) venting, it is not required.

There is already a vent established as the 2 inch pipe is going up the wall to what I assume is eventually through the roof.enter image description here

  • What plumbing code applies in your local area having jurisdiction? The do tend to differ in details, and those differences sometimes matter.
    – Ecnerwal
    Oct 9, 2023 at 18:41
  • 1
    Did you read diy.stackexchange.com/questions/116736/…?
    – popham
    Oct 9, 2023 at 18:51
  • 1
    @Ecnerwal i'm located in Ontario, Canada Oct 9, 2023 at 19:13
  • @popham I will give it a read thanks Oct 9, 2023 at 19:13
  • is there a better layout that might work? would prefer to use the vent on the sink side wall to vent the 3 fixtures if possible. Oct 10, 2023 at 19:37

1 Answer 1


You will have a correct wet vent if you use a double wye to connect the sink, shower and toilet.

The pipe's diameter determines the length of the shower drain. If you use 1-1/2" pipe to the shower, the max length would be 6'; if you use 2" pipe, the max length would be 8'.

The pipe to the sink needs to be a minimum of 2" in diameter. The pipe to the toilet can be either 3" or 4" in diameter.

enter image description here

Option without the use of a double wye:

If you are in a jurisdiction that does not allow double wyes installed on the horizontal, you can use a single wye so long as you have the depth to allow you to roll up and over the main line:

enter image description here

  • 1
    Does the drain pipe to the sink or the vent pipe to the sink need to be 2"? Most sink drains are 1-1/2" and would need an adapter to connect to a 2" drain line. Nothing wrong with going big, but it does take extra consideration. If you're stating that the sink drain requires 2", a code reference would be helpful, especially since I just plumbed my sink drains in with 1-1/2" and passed my inspection. (Yes, code does vary by location...)
    – FreeMan
    Oct 11, 2023 at 14:55
  • 1
    The pipe from the double wye to the tee for the sink needs to be 2". The drain pipe from the tee to the sink can be 1-1/2". The size of the vent from the top of the tee would be determined based on the distance of the vent.
    – pdd
    Oct 11, 2023 at 18:22
  • Thanks this is extremely helpful. So I understand, the double wye will allow air to flow from shower drain to the vent drain at the time the toilet gets flushed. This will avoid siphoning the p trap for the shower. Oct 11, 2023 at 19:34
  • Just read that in Ontario a double wye cannot be used horizontally. google.com/… Oct 11, 2023 at 20:17
  • 1
    @wintersoldier, sorry, that was a type. I meant 'a single wye'.
    – pdd
    Oct 12, 2023 at 16:35

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.