I’ve recently bought a house that I’m remodeling. The plumbing was done by the person I bought the house from but it has not seen water until yesterday. I added a slop sink in the basement and drained it into a pre-existing caped end that was there. After having the water turned on yesterday I checked all the sinks to make sure they worked properly and they all drained without causing me a reason for concern. Including the slop sink. I then filled the tub on the second floor to check for leaks there. Upon draining it I heard water running in the basement and found the slop sink overflowing, filling from the drain. After the tub was complete drained the slop sink stopped overflowing and started draining. At a relatively slow rate I would say. I’m wondering if there is a blockage between the house and the main sewer or is the slop sink not vented properly?

In the basement there is a 3” or 4” line that runs from the ceiling down into the basement floor. Approximately 18” above the basement floor there is a reducing tee with a side entry of 2 inches. This line has a tee in it with one leg going straight up into ceiling creating what I would assume is the venting system for the house and the other leg of the tee goes to a short run of pipe and then the cap that I removed to install the slop sink drain. This 18” above floor line is lower than the sink bottom but higher that the slop sink drain trap.

I hope I’ve given you enough information to answer my question as to whether this system is vented proper?

Hi Troysnader...

The slop sink definitely needs its own vent! You can run an individual 1.5" vent just after the PTRAP and connect that to a vent from upstairs or run it into the attic and connect into a vent up there... or, if code allows it in your area you may be able to install a air admittance valve (AAV...see picture below). It can be piped similar to the 2nd picture posted.

That being said... I am also going to suggest that there is probably a clogged drain pipe here as well. To determine if this is a clogged main drain line I would have you remove the MAIN DRAIN CLEANOUT (4" brass cap at front of house if city/town sewer or at rear of building if septic system... usually) and then I would have you repeat the tub draining test and see what happens. If it overflows the slop sink... issue is at pipe from tub/slop sink going into the ground. If it overflows or backs up and out the main drain cleanout then you have a main drain line clog and the drain line will need to be sanked to clear the blockage.

If it overflows the main drain cleanout then have someone come in and snake the drain... see what they find. Then you may want to have the drain line videotaped so you can be sure of exactly what condition the drain line is in.

If drain guy finds roots then previous homeowner has some explaining to do as root issues should have been disclosed prior to sale of home.

A ventless slop sink would not cause the tub to drain pporly... would cause sink to drain poorly... just so I am clear about that!

Anyway... check out the stuff I mentioned... let me know what you think here...

MARK