Question about vu4 air ride manifold

[t76turbo]

I have the vu4, porterbuilt bracket with viair compressor and 3 gallon tank. I had a leak in a pipe plug in the end closest to the cab and couldn't get a tool on it to remove the pipe plug to reseal it.

So I put extra air in the bags to give me more room to get to it and removed 3 bolts to drop the end of the tank. When I drained the tank the bags lost all pressure and dropped to the ground.

Just side note. I only have bags in back now and have the front bags and PB lower control arms with the drivers side compressor bracket, tank,and compressor waiting to be installed. So for now the ports for the front are capped till I put the bags in. I am building a big block with Chris Straub cam and 049 casting heads now and am going to install all this at one time.

I thought the vu4 would hold pressure in the bags even if the tank is empty. Am I wrong??? I plead ignorance.