overstocker: Mine is just snug fitted too. I did check to see if the hole was clogged but it is ok. Maybe it did it before but I might have lowered my return nozzle when I moved the tank. I have been experimenting with different water flow direction.
If I shut the pump down and then lift the nozzle up, it stops draining.
clean tank: Good idea on the check valve but I have been told not to rely on one.
*180 gal Display, 100 gal basement sump, 33 gal refugium, 3x250 MH, 2x160 VHO actinics, zoos, some softies, LPS & lots of acros and other SPS.
*100 gal prop tank plumbed into main system w/ 2x96 PC lights and 1x150 MH,