What way does an aquarium air pump check valve face?
Blow through it. One way will allow air flow, the other way will not. You place it in the air line so it allows air flow into the tank and stops water from draining back in the event the pump fails. The check valve I have has an arrow. There is no standard color code, so the fact it has a black and a clear end means nothing. You will not hurt anything by simply trying to blow air through it to determine which way does what.
