2nd floor bathroom sink drains down to about 3"
Our 2nd floor bathroom sink drains down to about 3" of water in the bowl each time it is filled, but won't drain farther. 1st I plunged it (not sure if this is still the recommended 1st line of action or not). Plugged the sink vent hole and black water comes up. (Gets even higher in the sink bowl).
I removed the P trap, and cleaned out what little was in it, and tried to run a snake down the remainder of the drain. It went in about 2 or 3 feet, but I could not get it to go farther. The house is almost 100 years old, by the way. Metal pipes. It was a hand-operated snake - just a coil of wire with a length of metal tube and a set screw. So I probably gave up too soon, but it didn't seem possible to get it to go any farther, although it still turned fine.
I replaced the P trap and tried plunging it again, but no different results. Just slightly cleaner water now. SO when I plug the drain with the built-in plug, and fill it over the level where it will drain down to, and then unplug it, it drains down fast enough to create a small whirlpool in the water. In fact, with the plug un-plugged, the water never gets above a certain level with the faucet on - it seems to drain almost quickly.
Is this simply a partial blockage that has enough gunk to stop a little water, but lets the water out with higher pressure? What is the down side to using a liquid chemical to unblock it? Would I be likely to damage the pipes? We've ahd very cold temperatures here the last week or so - I'm not sure if that could affect it. Or would it be something wrong with the vent pipe?
Thanks