Join Date: Jul 2010
Location: Outside Philadelphia, PA
In cases where we are talking about air lines, the best thing to do is to mount the air pump above the level of the tank. That way, if can't back siphon and you don't even need the check valves. You can get a similar effect by first running the air line tubing way about the level of the tank water and back down.
If that is not possible, get some of those quality brass check valves, like the ones they use on pressurized CO2 systems. The aquarium grade check valves are not the best quality and will fail sooner or later.
In all cases check valves must be tested from time to time. All it takes is a little dirt in one to keep it from working. Using an air filter after the pump can sometimes help.