The smaller U-tube definately worked good. Just some issues. I believe the Eshopp's stock U-tube is 1 1/4". First I tried a 1/2" (which I thought was 5/8"). It worked well, as I watched any bubbles zip thru the tube, yess! The only problem was the water level in the DT rose to the rim's plastic lip.. umm no! Next I tried a 3/4", which also worked like a charm. The water level stayed where it should. The only problem is the 3/4" tubing has no elasticity! Whe the tube bends, it narrows or flattens a little, which I don't see a problem, but because of the elasticity, it was pushing outwarrds on the overflow box (which wsa slanting), and I was afraid of the acrylic cracking, and the box coming undone and a flood. I'm at work right now and I am bending the tube with rubberbands, so I can get it permanently bent. Then I will use this tube and also try lowering the box.