Why doesn't my T airline splitter work?
If you are using a T-splitter to share one air pump with two devices, sometimes air does not travel down one of the outlets. One of two things could be happening. In the first case, your pump is not strong enough to push air into more than one outlet. In the second case, the air always chooses the path of least resistance, so you need to install air valves (plastic or metal) on each path to ensure that air reaches all the devices.