Pretty simple and self-explanatory. I have used this for years. Embarrassed to admit how long I've used the same one, in fact. I lower the stopper in my bathroom sink and place this over it (have to lower it to prevent gaps that a lens could sneak under). Works great.
The BEST approach is not one of these rubber things at all. It's a generous sized terry towel over your whole sink so that your lens can't accidentally strike porcelain and crack (for example). Lenses are much less likely to bounce when they hit a towel than virtually any other surface.
Me, though, lazy, and old habits die hard, so I will continue using this. I do all my lens stuff over the counter, not the sink, so mostly I'm concerned about the lens rolling down the drain if it's not covered.
I bought one of these to reach free shipping on an order, but it turned out to be one of my best purchases. It's always in my travel kit - and has been invaluable at campsites and overseas where you never know what the sinks will be like.
I bought 2 of these, 1 for home, 1 for travel and it literally saved my lenses from fall I down the drain. This is much better than using paper towels to cover the drain. NOTE FROM REBECCA: Thanks for posting! I've used a towel but... with hydrogen peroxide solution that's not a great approach LOL! - Rebecca
I got one of these a few years ago (mine has a slightly elevated center to go over the standard sink plunger type closure) and I use it when removing and cleansing/rinsing my CL daily. So easy to pack with CL supplies when traveling. Can be a lifesaver when CL falls into sink.....just saying…. NOTE FROM REBECCA: I once had a GP lens shatter in a porcelain sink. Ugh! Thanks for mentioning about the elevated center - I will poke around to find some more designs. I tested a couple of different ones a few years ago but they were enormous, and then I kind of forgot all about it. Funny thing is, I use this blue one every day myself with my EPP sclerals and every day I have to maneuver it just so to make sure it covers that gap on the side of the sink I'm working on but did it ever occur to me I could find a better product? Noooo. - Rebecca