drain-waste-ventplumbingsink
Sometimes our bathroom sink will drain so slowly (with the water running) that the water will fill it faster than it can drain.
However, after shutting the water off and letting it completely subside, it will typically drain properly the rest of the day and for the next several.
Then after a few days it will repeat its previous behavior.
Running Drano through the pipes has not seemed to have made a difference.
What could cause this behavior?
This might not be the answer, but for reference here is a problem that can occur if the plumbing is not installed properly.
If you look at Fig. 3, this is what a proper drain looks like. You'll notice the orange line represents the water level in the system, the water levels out in the trap preventing sewer gases from entering the sink drain.
In Fig. 1, you can see what will happen if the drain line has to go up before meeting the main drain line. Again the orange line represents the water level in the system, and as you can see the water level is much higher in the drain.
Fig. 2 shows what could happen if the sink was installed lower than the rise in the drain line. The water would never fully drain from the sink, since it would require extra pressure in the system to push the water up the drain.
I wouldn't guess this is the issue in this case; since as you can see, if you opened the trap in this case you would have more water drain than what is typically in the trap.
In a perfect world Fig.1 and 2 would never pass inspection, but as we all know not all plumbing is properly installed and/or inspected. So this could possibly be the case in this situation (given the plumbing was installed by an amateur plumber), but it is doubtful. It would be more likely caused by a clog in the line.
This has been an ongoing problem in the bathroom sink we use the most. When I was using conventional solutions (Drano and the like) to unclog it, I just assumed that there was a bunch of hair in the drain. This was a problem every couple of weeks, though, and I hated spending so much money on toxic drain cleaners. A couple of years ago, I happened across a long and flexible, toothed tool called Zip-It at the hardware store, and I've not had to invest in drain cleaner since. Since this tool pulls whatever's clogging the drain out of it, I learned that it wasn't only hair causing the sink to backup - it was also tons and tons of black slime. It's pretty gnarly, but it's satisfying to know that I'm actually physically removing this stuff from the drain! I saw that the tool is sold online as well, and I noticed that it's marketed in some places as a one-time use tool, but that's ridiculous. I've used the same one since I bought it two years ago, and it still works as it should. It's really cheap, though (I think I paid $3 for it), so even if the teeth do break off, it's easy enough to buy another one.
That drain still clogs with black slime every couple of months, and even though I can pull it out, I'd like to prevent it if possible. So, I'm going to start using baking soda + vinegar + hot water to see if that works to prevent it.
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