if your near an airport talk to an authority there. fuel sumping airplanes is very common and the used fuel is disposed of. 20 gal of fuel is a drop to a 50,000 gallon airplane. youd have to do a general aviation airport though. Commercial is WAY to restrictive with EPA regulations. Have you spoken to your local gas station? They might have some set up .. Firestation?
If @ 1st you don't succeed, grind it, hammer it, weld it, drink a beer and try again.