With regard to silicone and polyurethanes...
I'm sure many have different preferences but what are your methods? Those
cartridges can seal up in days and it would be nice if one could keep them
say a month when you know you are gonna need more of it.
Best I've ever come up with is putting a small piece of plastic bag over
the cartridge tip and put one of those yellow cartridge caps on. It still
will seal up but not quite as bad. Once a week open it, get rid of what has
dried, squirt a little fresh stuff out and recap.
Of course, best solution is probably suck it up, toss it out and pop for
another 4-6 bucks depending on the product.