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shower drain below slab
shower drain below sla  
QUESTION: I intend to add a bathroom with a shower in the basement of my home.  The original owern/builder had the foresight of adding a bathroom in the basement and had the toilet already stubbed in and also a vent pipe resided two feet away - so I presume that has to be the vent for the toilet and drain for future sink.  I removed the concrete/gravel in the area where I want to put the shower drain with intentions of tying into the 3" toilet drain.  What I uncovered was another pipe (2") that was capped off right by the 3" toilet drain.  Was I this lucky that the builder actually laid waste pipe for a future shower as well?  I want to make 100% sure that this is a drain so I removed the cap on the 2" and placed an elbow and poured a bucket of water into it.  The main stack is about 8' around the corner and it has a threaded cap.  I removed that and listed to hear for the water draining.  I did hear the water drain as loud as day.  My question are these: Can I presume this is an adequate drain to use for my shower or is there another reason/function for this pipe that I'm ignorant about?  If it was intended for a future shower addition wouldn't it have been stubbed up through the concrete as the toilet stub was?  Am I correct in my thinking about venting this to the toilet/sink vent as I have it drawn?  I'm uneasy about just using the pipe and assuming that it was meant for a shower drain - after all, what are the odds that someone would actually choose that exact location for a shower and actually finding it without even knowing it existed under the slab?  Thank you, Randy

ANSWER: Randy- You know the saying to good to be true.....? There is, though, a slight chance this drain does go to main. And the sound of it draining in the 3" pipe is promising. You would have to have a sewer scope done to confirm. My belief based on your writing is that you are a lucky man indeed. As well are you planning a primer line to the shower trap?
Feel free to contact me for any reason.

---------- FOLLOW-UP ----------


Thanks for the quick response.  I'm sure by listening into the main stack by the threaded cap (main stack clean-out access opening?) that the water from the 2" pipe was in fact draining into the main stack.  I poured a 5 gal. bucket and the noise of water rushing into the main pipe was very audible.  I just didn't want to assume that the 2" pipe didn't serve a different fuction that I was oblivious of.  I think just to get further proof of it draining into the main stack that I'll again open the side cap (as sketched in my photo) and hold a mirror into the stack and with a flashlight look to see if I can get a visual of the water draining into the stack.   So with this visual proof (which I presume is all a sewer scope would give)would this be confirmation enough that I can use the pipe for a shower drain or is there a plumbing fuction that I'm not aware of?

After all, I don't know what I don't know.  Case and point - I had never heard of a primer line for a floor drain until you mentioned it in your response.  I'm not sure if code required me to do so, but it seems the prudent thing to do now while under construction.  I think I'll plumb a primer line from the sink trap.  Does this sound like the best idea? What type of line (material) do I need to use to go into the floor to the shower trap?
Thanks again. Randy

The 2" pipe would not serve anything I can think of and would be the right size for a shower. I think you are on to something. get confirmation and go with it. as to the primer line -it is a wet line from water supply that keeps water in the trap(below grade) so that it does not dry out and let sewer gases out into the room. Ask your local pro plumbing supply house. they should have a kit available.

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Glen W


I can answer questions about the whole home building, additions and renovation processes. I am able to talk about finite hands on skills to budget and management areas.


I have been a General Contractor for over 25 yrs. and in 10 States

BA - Architecture

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