Sounds like you have a dangerous situation.

Your bilge blower should be set up to ventilate all the bilge areas. If not
then the vent system wasn't installed properly.

I would recommend that you not only wash it down good but you should rig
some gasoline safe ventilation to run until it is safe. If there is going to
be any welding or spark producing work done to get to the tank (defuel the
tank), you should have it tested as 'safe for hot work' by a qualified
person. If it is in a commercial yard they my require this as well.

Steve
s/v Good Intentions