But it's easier to just refuel the lower tank first. After filling the upper tank and then filling the lower tank with the fuel selector on both-172 or on-150/2, the resulting fuel outflow from the lower filler outlet once the lower tank is filled will reinforce remembering the better procedure.
This phenomenon is very hard on smokers
If you leave the fuel selector off on a 172, the engine only runs for about 15 seconds -- did that once too
