Hello,

I have a 2002 GS500 and today I noticed that under the tank, there is this nipple with nothing on it. Pic here: https://imgur.com/a/IAlf4Xm

Is this where the tank drain hose should be? If so, can I just throw any piece of hosing on it, or does it need to be something special?

any hose is OK, just route it down  by the right footpeg with the other hoses.

Yes, any hose routed down below the engine will work....Or just leave it off. Unless your GS500 is a garage queen show bike, the couple drops of gas that will dribble out of the overflow over the life of the bike isn't worth worrying about.

Thanks Bluesmudge and herennow!

Yeah, I really don't care about keeping the bike looking nice -- I just thought it may be a safety feature.

It is a safety feature. I'd urge you to fit a hose and route it to the lower part of the frame so that no fuel can spill on the hot mechanicals below the tank.