In working on finishing our basement, I've come to the bathroom. It was originally plumbed with the plan of having the fixtures share a common wall (vanity, toilet, then tub). so there is already a pipe going up the wall where the vanity would be, with a stub for the vanity drain. And there is already a toilet stub in the floor, and a square full of gravel which I'm presuming is to give us freedom for whatever tub we ever installed.

If it matters, this is a concrete basement floor, and I believe the main sewer/drain line for the house runs directly under this room, likely under these fittings, in the order listed. It's 2 year old construction, so everything is PVC. I'm familiar with the ideas involved in moving a drain in concrete.

We want to convert the tub into a corner shower, and move the toilet to occupy where the end of the tub was. (I'm also sliding a wall out. Great thing about unfinished basements...) I expect when I get under the concrete, this will involve about a 4'-5' branch from the main sewer drain out to the new toilet, rather than extra pipe and bends to connect where the original toilet drain was.

My question is what (if anything) do I need to do for a vent? Can I just run over to the wall behind the new toilet, come up into the wall, then run around to the existing vent? Would it be okay to leave a vent out?

Here's a terrible drawing, so you can see what I'm trying to describe... drawing of bathroom, as it exists and with proposed new toilet shown

I expect there to be further details needed, like I -think- that vent pipe is 2", but I'm not sure. I've had this question rattling around in my head, trying to figure out how to get all the detail in, and finally just decided to ask with some and fill in if something's needed.


  • Do you have enough headroom to tee the current vent and run it to the toilet wall (sloping it 1/4"/ft towards the current vent and thence down to the relocated toilet stack?
    – HerrBag
    Mar 23, 2013 at 19:20
  • @HerrBag I've got a typical 8' wall. for that matter, I could arrange horizontal runs in the joists, if I needed. But I expect coming several feet up the wall then running around the room would be fine?
    – Scivitri
    Mar 25, 2013 at 16:30
  • Dry vents are very flexible compared to wet vents, AFA routing goes
    – HerrBag
    Mar 25, 2013 at 19:27

1 Answer 1


You must have a vent. The toilet will not flush properly without one, and there will rarely be enough water left in the bowl. You need a 2" vent to take off from the branch line within 6 feet of the toilet. It can run up any convenient wall until it is above the toilet's flood level. Then it can run near horizontally (1/4" per foot) anywhere to tie into an equal or larger vent.

There's any number of ways to properly vent a toilet, and several common ways that are technically wrong, and even more that are just plain wrong. It's impossible to suggest a good method without a lot more information.

  • sigh This is of course the answer I was expecting. I think the connection in the floor, where the vent connects, is what I was hoping to avoid. I'll do more research about doing this right. ^_^
    – Scivitri
    Mar 25, 2013 at 16:34
  • In the UK we would use a air admittance valve close to the WC if the bench was more then about 12 feet. However our drain pipes may be larger so more forgiving.
    – Walker
    Jan 28, 2016 at 17:02

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