You should be able to loosen a PVC nut by hand, turning it counterclockwise. Wrap a towel around the nut to help you get a better grip on it. A metal nut may also require the use of a pipe wrench or large adjustable wrench. If you wish, you may also be able to disconnect the drain pipe at the top of the trap (the U-shaped bend) in order to give yourself more room to work with.
You may be able to hold the pliers with one hand and loosen the nut with the other, or you may need to recruit a helper. This would be a good helper job for an older kid or teen. If you have trouble squeezing the pliers, you can also insert the handles of the pliers into the openings of the strainer grate, then stick a screwdriver between the handles and hold it steady to immobilize the sink strainer. [2] X Research source
There are also locknut strainers with screw attachments, in which 3 or 4 screws are used to help hold the locknut tight against the underside of the sink. Bell washer sink strainers have an outer bell-shaped “shell” that fits over the entire strainer. This bell housing is pressed against the underside of the sink by a nut located at the bottom of the strainer (just above the nut that connects to the drain pipe below). [3] X Research source
Once you remove the screws, you should be able to loosen this type of locknut by hand. Turn it counterclockwise until it comes off the threads and slides down off the strainer. If the entire strainer is spinning when you try to loosen the locknut, use pliers to pinch (or pliers handles and a screwdriver to hold) the strainer still from topside. Use this method with any type of spinning sink strainer, locknut or otherwise. [5] X Research source If the screws are hard to turn, then spray some WD40 onto them and wait 5 minutes. This should help to loosen them.
If the locknut is completely rusted in place and simply will not come off, you can use the cutting wheel attachment on a rotary multi-tool to slice through the locknut, then (if needed) a chisel and mallet to split it apart. But you may also want to consider calling a plumber at this point. [7] X Research source
If the bell housing refuses to pull free easily, wedge a flat head screwdriver into the gasket sandwiched between the bell and the underside of the sink. Pry the bell housing free and pop it off.
If the strainer won’t break free, tap it from the underside with a mallet until it pops loose. If you have to bash too hard, though, you may damage the sink itself, so consider calling a plumber if necessary. Scrape away any dried putty or other gunk from the rim of the sink (both above and below) if you intend to install a new strainer. Use a plastic putty knife so you don’t scratch the stainless steel finish. [10] X Research source
You can buy plumber’s putty anywhere that sells plumbing supplies. Make sure you have cleaned away any old putty from the sink surface with a plastic putty knife.
If you’re reinstalling an old sink strainer, take the old gasket(s) to the hardware store and buy identical (but new) replacements.
For a locknut strainer with screws, you only need to hand-tighten the locknut into place. The provided screws are what will press the locknut tight and hold the connection together. For a bell washer strainer, place the bell housing over the strainer, then feed the provided nut onto the threads at the bottom of the strainer. Use a wrench to tighten this firmly (but again, not excessively).
If this spot passes the “tissue test,” let the water out of the sink and run a dry tissue around the nut that connects the strainer to the drain pipe. If it stays dry, you’re good to go![15] X Research source
