I put red food coloring in some water and filled a tygon tube
tube about half way up with it. The tube rests on the floor
and is taped to a door jamb. The other end of the tube is hose
clamped to the vent tube on the bottom of the tanks.
As of this writing I've tested 2 of the 4 tanks. Both leak!
I found the leak in the first one, which leaks down in about a half hour
On the second tank, the leak is much smaller. It leaks down about an inche
of water in about 2 hours.
I've been using soapy water and a paint brush to search for the leaks
but so far haven't been able to find it.
I haven't tried to seal the leaky tanks yet. My plan is to find all
the leaks first.
I'm not sure how I'm going to fix them. My hands don't fit through the
filler.