Better idea when testing tanks.  Seal off all outlets.  Take a latex glove,
tie off the hand opening, cut a finger and attach   it to the overflow vent.
Blow air into tank via fuel line.  have gas cap sealed.  Make sure it is
trully sealed.  They leak.  Tape it shut and test for leaks at the glove,
vents, all seams, fuel cap. Inflate tank till glove blows up. measure
initial diameter.  Measure again at varied time periods. diameter should
stay the same if barometric pressure remains constant, else you have a leak
or barometric pressure changes diameter.  This very low pressure concept
will still demonstrate air leaks with a water and detergent solution applied
with a plastic squeeze bottle on all seams and save you the grief of
exploding your work.  I simply blew up the tank and glove  with my mouth
like a balloon.

To repair identified leaks I used a vacume cleaner attached to the fuel line
outlet. Be careful to not collapse the tanks, let air escape. so as not to
use full force of vacume cleaner.  Some attachments allow for an adjustable
air leak to reduce pressure.  Use it.  You only need a slightly negative
pressure differential to allow the epoxy to flow.

Heat up epoxy and place it in a sryinge (sp) and inject the epoxy into the
identified leaking area.  The vacume will suck in the epoxy easily. Remove
the pressure so the epoxy remains in the affected area.  Test again after
curing epoxy.  I too tested the tanks for a few days after initial setup.
No leaks are confirmed with a full balloon ie full size glove.

Bob Smiley
N94RJ