We had a leak under the kitchen sink so I tried to do it myself. I bought a new sink strainer but forgot to install the gasket that goes under the sink in between the bottom part of the strainer and the actual sink. Can I live without it or should I undo all of it and install the gasket? There are currently no leaks so im hoping to leave it.

How hard is it to replace? Remove tailpiece, remove large nut, put in gasket and reassemble. Unless you have something really complicated it should be less than 30 minutes. To fix.

Brian gave you top notch advice. Don't forget to run a ring of plumbers putty around the lip to seal the top section. Good luck, Tom

Well, I must say, I do agree with Brian and Tom. But I also understand that in some situations it may be a "job" for a homeowner to do. So: if you put plumber's putty between sink and upper flange of the strainer, than yes, you can live without the bottom gasket. In fact, some of the new strainers come with only a paper gasket which is not really a gasket but a Go-Bo piece of material. Its purpose is to make the locknut slide on top of it when being turned and tightened against the sink.

Hope that helps

Milo

you can live without the bottom gasketI guess plumbing must have passed me by. I would NEVER Leave a metal to metal joint unless it was a ground joint union. I'm confused by Milos answer. He seem to say that if you use plumbers putty on the upper flange you can forget about installing the lower gasket but if you install the lower gasket you don't need to putty the upper flange. Either way that leaves a metal to metal joint that, in my opinion, will cause a leak and that Go-Bo gasket he's talking about is called a anti-friction gasket.
Bottom line, I would never install a strainer without using all the parts shown in my image. Cheers, b Tom