Do I need check valves?

[Jono]

i just installed some jabsco pumps. I've only tested this out once and wonder if I have a small problem here.....
Its hard to know if my pump is actually draining because it does this from the bottom of the boat and there is no audible cue. When I went to empty the bag, I could swear the pump was just sucking air through the vent. I had to press down on the bag's fitting to get it to prime like i do with the over the side tsumami's. Would a check valve solve this?

[Neverenough]

Is your fill/drain hose on your bag at the lowest point? For the jabsco to suck the water out the hose will have to be at the lowest point on bag so that it can pull the water out. Kinda like trying to drink a big gulp with a regular size straw! Also check your hose fitting and clamps. If your sucking air it will not work either.Hope this helps.

[Jono]

I have the fill/drain on top fitting of the bag. i'll move to the bottom and see how it goes.

thanks