I have a problem with the drain in my bathroom sink. With the drain open, the sink fills with water until the water level reaches about ½ inch from the overflow drain, then suddenly, as if the drain were opened, the sink drains empty but then the entire process starts over again. I have really scaly water so I thought that the overflow drain might be blocked so I cleaned out the overflow drain with a wire hanger. Although I removed some residue, I’m certain some still remains and it didn’t fix the problem. If it is the overflow drain, how can I clean it out? I thought it might be a problem with the vent to the roof but the tub and toilet in the same bathroom appear to drain fine. Any ideas?
Darge
Replies
Disassemble the drain from the basin all the way to the wall and check everything... especially the trap. If the tailpiece, trap, and arms are clear then reassemble and consider adding an air admittance valve ("vent valve") under the sink. Check the actuator for the drain stop, since those collect a lot of stuff. Don't assume that just because other fixtures are vented that the sink is. There are lots of wrong ways to install vents and they are easy to find in newer and older houses.
You guessed correctly about the ven being the problem.
Typicaly sink, toilet and tub go to a common vent, ussualy located close to the large waste line for the toilet. The other two vent lines tie into the larger line above the highest flood plain (sink). What you are describing seems like a partial blockage of the sink vent where it tees into the lager line. Doesn't affect the other two fixtures because the blockage (partial) is only in the sink vent side.
If you have access to the soil line from below, try running a drain snake backwards, up the drain and into the sink vent. This should push the blockage into the larger DWV, where it should (hope) was on out.
Dave
If the trap adapter is at the wall line, you can usually get a snake started upward with a little effort. From there I would expect one vent 90 and then a short horizontal run to the tee into the main vent. Worth a try, but I'm not sure how fruitful it will be. If in fact there is something in there I would probably try to flush it down with water run down the vent from the roof after you snake as far as you can.
I've seen plenty of bathrooms where the lav was not vented until below the floor, rather than having the proper riser from the trap tee. I'd still say the first play is to break down and inspect the trap parts.
I would probably do likewise. My general luck with a drain snake is for it to go up the vent, when I want it to go down the drain. That generally happens when someone puts in a straight tee, instead of a sanitary tee. I also use a pump up type air plunger on sink drains. Works pretty well on smaller drain lines. I have even used a CO2 bottle to give them a blast of air. Have to be carefull with either of the air methods. the blow back or out at other fixture can be real ugly.
Dave