5 to 7 psi translates to a minimum  of  720lb/sq ft on every square foot of
the wing skin.  That is a lot of force trying to burst the tank.  I would
say that pressure is an accident waiting to happen.  Also what other joints
have you strained that you cannot see?

IMHO 1psi is more than enough to show up any leaks.  I used that and found
one leak at the rear spar attachment bolts.  I also used a home made
manometer to measure the pressure.  It was of such a length that it would
blow out all the water before the applied pressure burst the tank.  An
interesting feature of the manometer is that it reacted to the barometric
pressure rising and falling which  made me think I had a leak after I fixed
the first leak.  It seems obvious to me now but I spent a few days chasing
non existent leaks.  This point demonstrates the sensitivity of the skin to
fairly minor changes in pressure.  Incidentally I held my pressure for 36
hours in the final test before I dismantled it.

Ian Crowe
C-FKRO 360 75 hours