Basement Bathroom install

[Ben Hatcher]

I'd like to install a lavatory in my basement. I don't have a plumbing rough in for a toilet, but I do have what looks to be a 3" pvc pipe stup coming out of the slab. I presume this ties into the sanitary drain system. The main stack is maybe 15 feet away. Can I put a lavatory in and tie into this pipe? Is it too small? What are the odds that there's a properly sized pipe under the slab with this smaller pipe sticking out of it?

[Dan Hintz]

Ben,

It's likely this was meant as a drain for a washing machine (and similar)... to know if it attaches to a larger pipe downstream you'll have to send down a video scope. We have something similar, though I believe ours to be a 4" stub... it's currently being used for the washing machine drain, but due to its somewhat convenient location I'll probably turn it into a bathroom drain. Some slab will need to be chopped into to add a new washing machine drain point, but thems the breaks!

[Ben Hatcher]

Mine was probably intended to be used for a utility sink. Something tells me that I'd rather not bother break up concrete to put in a toilet.

[Prashun Patel]

I think u should take yr project to TerryLove.com. They helped me through a DIY basement installation.

That being said, the appropriateness of what you have/need is dictated by yr local codes. You should 1st consult yr local construction office and be sure they allow homeowner plumbing mods.


In my area (Central NJ), a 3" drain to the main 'stack' is fine.

If your basement is truly pre-plumbed for a bathroom, then you should see several stubs coming up: one for the toilet (3"), one for the shower (1.5-2") and one for the sink (1.25-1.5"). You should also see vents coming up for the toilet and shower. If you only see one 3" stub, then it's likely intended as a floor drain or laundry drain, which wouldn't be vented.

The good news is that you appear to be half way there: The presence of the stub implies that at least yr plumbing leaves the house below the basement slab, or you have an ejector pit already installed. That's 1/2 the battle. Actually, builders rarely get the homeowner's needs/desires right when they do rough-ins anyway, so you'd probably have to do some trench work to reposition the lines anyway...

In fact, if you don't want a shower, you'd only have to excavate a little around the stub to tie in a vent (upstream from the stub) and the lav drain/vent.

I doubt it was intended for a utility sink. That'd be a smaller pipe, and would require a vent

[Ryal Cox]

I would verify that the 3" pipe actually goes into the sanitary system. Many new houses have a 3 or 4" pipe going through the slab for radon venting. Just a thought.

[Prashun Patel]

I would verify that the 3" pipe actually goes into the sanitary system. Many new houses have a 3 or 4" pipe going through the slab for radon venting. Just a thought.

I doubt the radon would vent INTO the basement; it'd likely go up and out the roof.

[Peter Stahl]

Best thing to do is call a couple Plumbers and get a estimate. You don't want sewer gases coming back into the house or worse yet sewage.

[Ben Hatcher]

Peter, that was my next step. I just thought I'd take a stab at the chance that someone on the creek might have some insight into standard practices and what that pipe might be for.

Ryal, it isn't a radon vent. It is in the center of the basement and is capped.