leaks gas out of drain tube when petcock is left ON
I had that problem, too. Never had it until some guy replaced my tube: evidently it's a non-standard diameter. You can get the right diameter (it's just plastic tubing) at Home Depot, but even though that fitted the way the old pipe did, I still had leaks.
Don't bother with the spring-style (left in picture) tube clamps: they can be made to fix the problem, but you basically have to use one several sizes too small, fight to get it on, and get clever with where you put it (put it all the way back near the end of the metal fitting so the end of the plastic hose presses against the base of the fitting). There's snap-on style clamp (right in picture) that's a little more exotic, but also did not completely solve the problem, and was even more of a pain to take on and off than the spring-style one.
I finally broke down and bought a small hose clamp, screwed it down tight around a bolt that was about the right diameter (to bend it to the right shape), then applied it to the fuel line. It now takes a screwdriver to get the gas tank off, but it seems to have fixed the leak (maybe).
The real solution? Turn off the fuel (remembering to turn it back on is the harder part, and can be extremely embarrassing).