A few things, probably cause I was trying to re-use old parts. The stopper was old and worn out, the tank was old and the tank throat was larger than it used to be, so the stopper did't really plug it, I used stopper plates with holes for 1/8" tubing, and mixed 1/8" tubing and 3/32" tube, and, possibly the cause, I'm thinking the tubing wasn't pushed on enough over the copper tube and barb, so there may have been an air leak there. So I just started from scratch, with new, correct parts. Seems to have worked.