I would like suggestions for what to use as a pressure relief valve.

Problem:
Sealed, watertight hulls have leaks small enough to disallow water to come in, but large enough to allow presurized water to come in.

Scenario:
Warm hull is plugged before placement into cold water. Inside air shrinks and creates negative pressure, encouraging water to rush into normally insignificantly small holes.

Solution:
During the cooling process, leave a port open so air pressure may equalize as the hulls cool down.

New Problem:
No ports on hull besides the sub-surface drain plugs.

Solution for new problem:
install a tiny pressure relief valve on each hull. Valve should be small, light, Normally Closed, and temporarily opened.

(I am picturing it to be either a small twist or a push button action.)

Seeking Ideas on what I might consider using for this valve. The valve must offer all of these functions:
1)let air to move in
2)not let water in
3)not let pressurized air out.

I'll start the brainstorming with this idea:
Drill a tiny hole (1/32" or 1/16") in each hull and cover with duct tape.

GARY