I think you're referring to your filtration system, if so...
put one end in your prefilter box, the one that sits outside of your tank, and one end in your prefilter cup, aka overflow box. Put some water in your prefilter box first, then push a siphonine tube up the end going into the prefilter box until it's about halfway through the curve of the U. Lean down and suck on the end until you get a mouthful of salt water basically. It sucks and tastes nasty. If you end up with an air bubble, keep trying until you don't. I have also found you can tap the U tube tube against the filter boxes and this sometimes will release any air bubbles. It may take a lot of tapping though. This will start your water flow, then you just have to keep an eye on your water level in your sump
