^not quite^I Have my pump sitting behind the tank roughlt level with the airstone in the tank. So no back flow problem here.
If your airpump is below the water line, you may have a problem.
If the tubing from the airpump were to be unplugged at the airpump and droop below the water line, you may have a problem.
If you really hate checkvalves, keep several loops of airline tubing mounted above the waterline between your pump and airstone. Loops prevent a good siphon from getting started. The only other way is to mount the airstone just below the waterline. That way, if it starts to drain your tank, it will quit after just a little water escapes.