How do I fix this sink?

PVC pipe is normally only hand tightened, just unscrew the top and the one on the right side of the picture. You won't be taking the whole thing off the wall, you will still have the straight pipe coming out of the wall. Make sure you have a bucket under the whole thing for the water that will drain out when you loosen the fittings. I am sure you can tell if there is another fitting to loosen to get the u pipe off, can't see the other side. Remember to only hand tighten the PVC or you could crack it and have a leak. Make sure to leave the bucket under the pipes and check for leaks when you have it back together. Once you take it apart once it gets easier to do. I had to clean my mom's pipes frequently in her apartment, it was all put together wrong because of where they had the pipe into the wall. It made the disposal pipes clog up all the time. Run a half cup of baking soda down the drain followed by a cup of vinegar. Let that fizz for a while, then follow with a gallon of boiling water down the drain. This will have the pipes sparkling clean of gunk. If that is in the bathroom sink, get a zip tool (thin plastic strip with barbs) that is made to get the hair out of drains like the tub/shower or bathroom sink. Do this to get as much hair out as you can before doing the baking soda/vinegar hack. I hope this helps you, Aaron!

Yup it looks like you have two places there to unscrew it.

The knurled nut on top and the knurled nut on the back side. Unscrew them both and unit comes off.

Both of the pieces with lines on them should unscrew then the piece(u-pipe i guess you called it) the trap should come right off clean it out then put back on & screw it back together. The piece coming out of wall should not move at all

what if the pipes leak after you screw them on by hand?

Hi Christine, Try again from beginning -Tighten it more! Did you have a washer that has now disintegrated? If so replace. If still leaking, use a cloth over the screw fixing and a wrench and turn carefully.

What you are looking at is called a bottle trap. Although I've not seen one quite like this before. Normally, the bottom 'cup' unscrews. The pipe coming down from the sink should go almost to the bottom of the cup, this allows the cup to fill with water to the point where the water can exit out of the side pipe - so that's how much water you will find inside when you undo the top and side nuts.

Behind each of these nuts you should find a plastic washer and a conical rubber washer - when placed over the pipe (it should be quite a snug fit btw), there is a chamfered edge which will end up sitting into the short pipes of the trap (facing away from the nut). As the nut is tightened, the plastic washer pushes the rubber into the space around the pipe inside the smaller pipes and this is what creates your seal. There is no need for undue tightness, if the thing leaks when hand tightened, buy new washers, they should only cost pennies.

I had to do loads of these when I worked maintenance in a nursing home, the carers had simply thrown food waste into the sink and tried to flush it away. I found the easiest way to clean them was to put a bucket underneath & take the whole thing off the underside of the sink and any pipe out of the trap for as far as possible. I could then clean them in the large sluice sink using hot water and a toilet brush. The brush was a lovely tight fit which meant the whole of the inside of the pipework got a good scrubbing as I plunged the brush in and out, rotationg as I went.