For the low price involved, just buy a new one for your make/model chassis. That condition is not right. If anything, the tank should be slightly pressurized from the action of containing fumes, as required by EPA standards.
2000 Winnebago Ultimate Freedom USQ40JD
, ISC 8.3 Cummins 350, Spartan MM Chassis. USA 1SG, retired;PPA,Good Sam Life member."We the people are the rightful masters of both the Congress and the Courts - not to overthrow the Constitution but to overthrow men who pervert theConstitution. "Abraham Lincoln"