In that case, I'll probably go ahead and order part# 7775K13 from McMaster Carr: http://www.mcmaster.com/#catalog/120/506/=vsm98h (in the "Quick-Opening Brass Check Valves" section). 0.3 psi seems much better than 1 psi.

I'm using Mobile 1, 5w20l. It's quite affordable at Walmart. They sell 5 qt containers, so I buy one of those and a 1 qt bottle each time.