Harbor Freight sandblast cabinet issues

[MJN]

Alright, I bought a harbor freight 40lb blasting cabinet and figured how bad can they screw up a sandblaster.
I found a ton of You Tube videos of guys modifying these things to make them work decently. They come with a siphon tube from the store which doesn't work- or didn't work at all on mine- which is my main issue. Seems everyone modifies them with a metering valve to gravity feed from the bottom of the hopper and run the sand hose outside the cabinet. I went ahead and made a metering valve for mine, basic copy of one I found on YouTube. For whatever reason the valve does nothing, I only get sand feed to the gun with the valve closed, even open a crack the sand drains back down and will not feed the gun. I first tried a full bag of blasting crystals (Black Blast recycled coal slag) but emptied the hopper and just added a few scoops. This seemed to help but still can't get steady feed to the gun to even get a small part blasted clean. It also will not blast or pull sand with any nozzle besides the largest. I also don't have a dust collector hooked up, I'm guessing this would help more with the leaks, even after taping and caulking all the seams.
Does anyone have one of these cabinets and had success making it work better?