here is a little project i made. it is made of 6061 t6, and i have tested it up to 100psi external pressure (equal to about 230ft of water. ) not even a hint of moisture inside. i put it in a container of water and pressurized it to see if water for past the o ring. i dont know what the max pressure it can take is, but i imagine its pretty high. the minimum wall thickness is about 4mm.