deez, it's pretty easy to get a good seal with those Dubros, just use the 3 part top with the rubber stopper and the bottom and top, as you tighten it squeezes the stopper and creates a seal. remember these tanks are designed to be leak proof inside a little RC plane while it is doing loops, barrel rolls etc. I am more worried about your pump, do yu have a Danner or a Eheim? In my dubro the water hits the opposite side with the Eheim 1250 and I have NO air in my system. I am still convinced yu have a leak in your impeller housing, try to mark your waterlevel in the dubro and keep checking it to see if it is dropping, a sure indication of a leak. Finding it is the harder part
