How do you let something "sit" in a drain, anyway?
If your drain is working properly, it's going to, you know, drain
Friendly little PSA, on a slight tangent: Most stuff that it says on the package you can flush, you can't. Well, I mean physically you can, but unless you've got a crush on the plumber it's probably not a good idea. Tampons/applicators, Kandoo wipes, some cleaning wipes, stuff like that. They'll clog the pipes fast. Good for my family, probably not so good for yours. Oh, and garbage disposals really
don't like cabbage leaves. I don't know why. And, of course, don't pour oil/grease/cooking fat down your sink.
Roto-Rooter sells a product called Pipe Shield that's supposed to help keep your drains open. It's not caustic or filled with chemicals; it's bacteria that supposedly eat the gunk. I don't have a clue if it works or not.