I’m planning to ad a bathroom in my basement. The house was built in 1999 and the builder installed the piping in the concrete basement floor. There is a 4“ pipe for the toilet, and two 2” pipes for a shower and sink. These three pipes extend out of the floor about 18”. There is a vent pipe that comes out of the basement floor and run up through the first floor. There is also a 6” pipe cut flush with the floor that has a threaded plug about 18” below the floor. I have not opened this plug but I assume this is a clean-out trap or a back-flow preventer. There is a similar pipe near the floor drain (opposite end of basement) that I have opened and it is a back-flow preventer. Here’s my question: There is an addition pipe in the bathroom area and I do not know what it might be for. The pipe in question is 2 or 2.5” and about flush with the floor line. The pipe has a threaded plug in the top and the plug has two large slots in the top that appear to be for a large Philips screwdriver. The plug threads also appear to a sealer on them. Any thoughts on what this pipe might be for??

This board has been a great source of information as I get ready to start this project. Thanks in advance, Pete

Sounds like another cleanout to me. Likely Tom will confirm that when he stops in.

Hey Pete, Listen to the Labman, he's correct. This is a clean out for the lavatory or tub drain line. Instead of a regular cleanout cover with a raised square your plumber installed a flush clean out cover so it would be handier to walk around. Best of luck, Tom

Thanks, Labman and Tom, for replying to my posting.
Pete