Hello, I am a DIYer and I want to rough in drain lines for a bathroom before the slab is poured for my garage. My question relates to the toilet and shower drain risers. I plan to stub up a 2" line pipe for the shower drain and 3" for the toilet, and then cut them off after the concrete is poured. How do I make room around the pipes so that I can slide the fittings down over the pipes after they are cut off flush with the concrete?

I hope this makes sense - thank you in advance for your help.

For the toilet, I would use a 4x3 elbow and a 4" riser. The shower riser would depend on how much room the flange you will be using needs. Wrapping the stub with foam sill seal works well. Do you have proper venting for those fixtures? A trap for the shower?

Thanks for the reply. I am planning on using a trap on the shower and proper vents.
I’m learning and working out my design. I’ll post a sketch when I have it all worked out.

They sell styrofoam caps for the stub ups or you can layer cardboard around the pipe and the tape in place

I would also suggest using a 4x3 90 for the toilet stub up it will make it easier for setting the flange

i'm with steve on this one.
4 x 3 elbow below the toilet. (yeah) it is perfectly legal to have a 4 inch toilet riser drop into a 3 inch pipe.
run the 4 inch higher than the finish floor and cap it there.
pour the cement floor right up to the 4 inch riser and cut it flush with the finish floor.
you then use an insert type flange (into the 4 inch) and secure it well.

for the shower drain, you can make a 6 x 6 plywood box that you secure around the pipe. it doesn't have to be pretty because you'll bash the wood out after. remember.. for the shower drain clearance, bigger is better. once the base is set you should fill in the void space with minimal expanding foam before closing it in.

you must leave room for the shower's trap assembly in the 'box'


you must vent the 'future' fixtures before the 'pour'



an actual plumber on site might be in order


.................. as well as the REQUIRED building permit else you face a special disclosure form upon a future sale

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

i understood that the trap would already be installed and the shower "riser" would be sticking up ??
BTW.. my definition of "riser" in this case would be the pipe from the inlet of the trap extending up to the outlet of the fixture.

Thanks everyone for the help. Here is the layout I have come up with - I would like to know if I am on the right track. I have talked to the county about permit requirements and I can get a plumber out to check everything before concrete is poured.

Can you run 3" up for the lav, install a cleanout, then reduce back to 2" for the lav sink ?

That way you have a cleanout that will take care of everything.

Out here the vent off the toilet can be a 2".

If possible I would put a cleanout on the shower vent line to cover the santee. Hopefully you will never need it but nice to have incase there is a lot of hair going down that shower drain.

Looks good to me otherwise. Others that are better at piping layouts may chime in with something else.

Thanks for the suggestions, Curly. I’ll make those changes.

absolutely PERFECT

layout should be in the 'how to' book



a perfect example of individual best practice fixture venting

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

that,s the beauty of unions.. cost has nothing to do with the function of the job.
i would love to be bidding against you in a competitive enviroment.
i'd be driving a tesla and you'd be driving a yugo.

a side inlet san tee at the base of the stack. dump the shower into the side and dump the lav into the 2 inch toilet vent.
voila.. a perfectly function bathroom layout. 100% code legal at maybe 1/3 of uour cost.

[www.homedepot.com]

That’s a great diagram
Depending on the distance from the sink vent/ main drain to the shower trap would determine whether or not the shower drain needs to be back vented as packy suggested



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What did I tell ya ?

Just had to wait for the east coast to wake up!

This works, but I also like Packy's option which is more simple and easier.

I also like Curly's idea of installing a CO on the lav drain especially in Packy's configuration.

The other minor observations from a non-pro.

- if that wall is an exterior wall, I would flip the CO to face the outside so if you need cleaning can be done from the outside instead of hauling the machine all the way inside and end up dripping waste water on the interior.
- do not cut flush the toilet riser pipe when concrete is poured, wait till finished floor is done, tiles or wood or whatever, then use a long recip blade and flush cut it. You will need an inside fit toilet flange to fit that inside the flush riser, beware that they make some inside fit flanges that has a little bit of bevel on the underside, don't use those, use the ones with a clean square angle so the flange will bottom right at the top of the pipe and the floor.
- the shower p-trap use all solvent weld joints, don't get those with swivel joints just because they are easier to position. You are pouring concrete and it will be difficult to access later, and once you cover it with the preslope you cannot get to it anyways.
- support all your piping carefully, I like to put bricks and tiles under every joint to prevent movement and settling. When they pour concrete these pipes will be carelessly disturbed.

Good point sum I’ve seen concrete guys make piping more crooked than Bernie madoff

I like it! I’m off to the store for fittings. Thanks everyone for all the help!



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It’s about 39” from the drain to the shower trap. Will that work?

The wall is exterior, so I will put the cleanout facing out. And I will keep in mind your other suggestions.

39” will work maximum is 96”

Yocumguy, what software did you use to make that drawing

AutoCad 2023, drawn from scratch

Nice work. Autocad is expensive isn't it?

It is, I believe about $1600/year. But very useful for a variety of projects and I use it for work, so pretty good value I think.