I bought a Marina Airpump a few months ago, last week I noticed that one of my air stones wasn't working, so I picked up the pump to inspect it and found out the air outlet on the airpump had broken off and was stuck in the tubing. When I inspected the situation making sure the other tube was secure that one broke off too.
The outlets are made of some cheap plastic, I could buy a repair kit for this airpump, but forget it. I won't ever buy their products again!!