A sink strainer is a metal or silicone sieve that collects debris to prevent it from entering the drain and clogging the lines. No kitchen (or any room that has a basin installed) is complete without a sink strainer.
If you want to use the basin for things other than simply washing your hands, you need to have a sink strainer or you will be looking at your drain pipes back flowing because of debris that is lodged in the drain somewhere.
A sink strainer is simply a perforated bowl that will fit right over the drain and will collect all the debris before it can enter the drain. While their predominant association is with a kitchen sink, you need a strainer even in your bathroom sink and also over your shower drain as a drain cover.
They are also available in a variety of shapes, depending on the application. You can get a plate strainer which will simply be a flat plate with perforations. You can also get a basket strainer where the perforated area is shaped like a bowl in which the debris is collected.
If you are interested in getting your hands on a good sink strainer, there are a few things you should not compromise on.
First of all, the strainer needs to be durable. Ensure you get a stainless steel strainer or a silicone one with a stainless steel rim. This material will not corrode or catch rust, which is important given that the strainer will be in constant contact with moisture.
Second, the perforation needs to be just right so water can easily pass through it, but no debris can enter the drain. The holes in the sieve should be about 2 mm in diameter, although I have also seen smaller holes in the market. I prefer it to be anywhere between 1-2 mm.
Third, you should be able to clean the sink strainer easily. Since it will be sitting in the middle of your sink, catching food debris, the strainer can also get clogged over time not from the food but from a buildup of grease and slime over time.
You should be able to remove the strainer every now and then to clean it with soapy water. Stainless steel is typically not too difficult to clean and also retains much of its original shine. However, it would also be useful if the strainer is dishwasher safe.
With these factors in mind, if you are ever out in the market looking for a sink strainer, you should not have too difficult a time finding one.
Remember, if a sink does not have a strainer, it is nearly unfit for use. You will have to end up spending a lot more on getting a plumber to clear out your drains if you neglect to spend a few dollars on a simple sink strainer. It is an elementary but effective device that will transform how you use your sinks.