David,
There is a pretty specific ratio of fuel (fumes) and oxygen required to result in an explosion, so I don't think things are quite as dangerous as they seem.
If you are going to have the gas tank cooked anyway, why not fill it with water after you drain it to purge most of the remaining fumes.
I went to a seminar put on by Standard Oil years ago where we tried to ignite a fuel/air mixture in a special chamber using static electricity as the ignition source...it was pretty difficult to do unless that ration was right on the money.
Stuart
Last edited by atomarc; 01/02/2009 12:16 AM.