plumbing dual port bags?

I have firestone dual 1/2" port bags and im not sure if i should run one valve to each port to fill or one valve to fill and one to dump?If i run two for up how would i run a dump,and whats the average psi to make it hop on one hit or is it even possible with only a 7 gal. tank and a 3/4 hp comp?thanks for any advice