Sand-blasting cabinets?

There is a clear rubber hose that attaches near the end of the gun, then a 1' long metal tube that attaches to the end of the rubber hose & gets buried in the media. None of it is clogged. It is blowing air out of it. When I bury it & hit the trigger, the media starts to "bubble" up because air is coming out of the tube & the tip of the gun. If I put my hand over the end of the pickup tube it does not suck it in, it blows air out. There is absolutely no suction in the pickup tube. I will try to take some pics of the setup & post them tonight if they help with my explanation at all.