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In answer to the posting by Craig I am in the middle of testing my tanks
and for what it is worth here is my ten cents, albeit in Canadian funds.

First two don'ts

1. I pulled a vacuum on one tank of about 10" Hg and there was a loud
bang!!!!  I had collapsed a portion of the skin between two ribs.  After
removal of the top skin I found that the foam core had cracked but the
inner skin was intact.  Repair job in process.  Since then I have limited
myself to no more than 3"Hg when required to suck epoxy into a leak.

2. When pressurizing a tank the factory told me not to use more than
0.5psi.  That's right, half a pound per squinch.  I had been using one psi
and it does not seem to harm anythig but you are on your own there.

To measure pressure you need a manometer or "U" tube make each leg about
35" long.  Steal your wife's sewing tape (if you still have a wife at this
stage in the building) and fasten it to a piece of board about 4 to 6"
wide.  Take a piece of 1/4" diameter clear plastic pipe and fasten it to
the board in the shape of an U aligning one side of it to the tape.  Make a
base to allow the contraption to stand vertically. Fill it with water using
a suitable food colouring (Canadian eh) to make the water level easy to
read.  Voila... one manometer.

Blank off your breather on the tank and use your fuel suction exit to
supply air to the tank and by means of a "T" connect the manometer.  Use a
fuel supply cock to admit the air or any other suitable means to cut off
the flow once the the pressurization is complete.

When pressurizing the tank I used shop air BUT THROUGH A REGULATOR SET AS
LOW AS POSSIBLE  USING A LOT OF CARE  to avoid blowing all the water out of
the manometer or worse still blowing up the tank.  You need to have 14"of
differential height between the two columns of the manometer for 1/2 psi
and of course twice that for 1 psi.  Go slowly, it is very easy to blow all
the water out of the manometer and I suspect just as easy to blow up the
tank. That would be much more spectacular than collapsing it and with much
more potential for injury to the operator.  I am only an expert in the
collapsing of tanks.

Once you have the tank pressurized the fun begins and I can do no better
than refer you to the recent excellent advice I received on this channel
from amongst others, Bob Chesley, Fred Moreno, Angier Ames, Neil Kruiswyk
and Paul Kapcin.  The last had the most elegant solution which was to use
freon or whatever is allowed these days as a pressurizing medium and an
electronic sniffer to detect the leaks.  But you still need the manometer.
As Angier noted the pressure will fluctuate with temperature and barometric
pressure.  I am into my third day at 25" wg and I am seeing pressure
fluctuations of 2" due to my space heater and the changes in the barometric
pressure.

The latex glove trick is an indication of the capability of the tank to
hold pressure and does act as a safety valve but the manometer is
definitive and cheap if your wife does not catch you..

The above is a distillation of what I learnt from the list and my own hard
won experience.

Ian (Fuel tank boom) Crowe