The last few times I used a wire wheel in a grinder. You only have to pull off whatever will come off easily by hand, and the wire wheel rips right through everything else. I don't try to clean off all the old adhesive, I just use some 3M adhesive cleaner to get any dust off the residue and stick the new gasket on top of it. If the old adhesive is hardened, you do need to remove it all, but it will come off clean and easy with the wire wheel. It barely takes a minute to get it all off, which is good since the crappy Ryobi cordless grinder I wasted money on barely runs that long on a charge.
I use a brass wire wheel so it doesn't leave steel particles embedded in the stainless which will rust, and I can use it on the tank where the gasket is going to seal to clean it up without leaving any marks.