This inexpensive homemade valve can be used to relief compressed air from a hull. I guess it is easy to modify for your specific purpose.
![[Linked Image]](http://www.catsailor.com/bb_files/144283-valvulafloats.jpg)
This is what is done on the floats (amas) of Corsairs/F-boats. My F-27 has one on each float near the front beam.
I have one per watertight compartment per float, six in total.
