The devil is in the details. Thinking about it for another few minutes
last night, I realized that I don't want to subject all these plastic
hoses, joint, and screwed fittings that I'm trying to keep absolutely
odor tight to pressure. If it was a steel tank with hard piping,
maybe. Even then, I would want a pressure relieve valve and those are
very low pressures to have one work reliably.

A wad of toilet paper going up into the (too small) vent on our
plastic tank could also turn this into a bomb that you don't even want
to think about.

Slightly off the subject:

I remember a shipyard here in Maine needing to fill the built in tank
in a
just completed fishing dragger with water to test it. The water at
the
dock was off so they ran a long hose down the hill from the shop and
connected it to the tank. They were smart enough not to hook it up to
city
water pressure and ran the water into a funnel. They weren't smart
enough
not to hard mount the hose to the tank and the vent hadn't been
installed
yet. The weight of water in the hose, with a vertical drop of about
25
feet, bowed the top of the tank up about 3 inches. Since this was
also the
floor of the crew's quarters, all the accommodations had to be ripped
out
and a huge section of the boat cut out and rewelded. It cost about
$100,000
to fix.

--

Roger Long