Re:fish tank check valve PICS.
 

I used those HALGEN ones for a little while, the checkvalves from Pet Cetera are better though, the HALGEN ones tend to collect intake manifold crap (kinda looks like Oil) and then it pools up and stops opening.....

Re:fish tank check valve PICS.
 

I have used those same plastice ones and at around 10 psi they seem to blow their tops off. First day I had mine hooked up it blew and took me a while to figure out why my car was running so dam rich. There was no vacuum going to the MAP so it thought it was at WOT when it was only idling.

Metal check valves solved that problem and I was able to boost 10 psi with only three valves.