Sump level staying below minimum level

I have a Oceanic 90g bow-front tank. It has a Durso set-up. I have a 1 1/2" drain and a 3/4" return. I have a 2 baffle sump consisting of a wet/dry filteration system and a holding chamber (not sure if that's the right teminology) I have a coral life skimmer mounting externally on my sump which btw is working like a champ). I am using a Danner Mag-Drive Supreme 9.5 950 GPH Water Pump for the return. I'm having two issues. #1 it sounds like a washer draining (worse actually)Sounds like I AM INSIDE a dishwasher. I already had a vent hole on the top of elbow in overflow (internal). I drilled it to make it larger, but that hasn't worked.When the water drains into the 1 1/2" hose you can actally see a 1/4"-1/2" inch gap of air to each side of the flow coming down the hose! There is no siphon obviously because it goes in my w/d filtration sump. The 2nd issue is that my sump level is running below minimum level. It's still covering both pumps (protein skim. and return). I originally had floss in there for polishing, the water looked incredible, problem is I had read that some sponges and floss can slow water to return pump. So I removed it (water quality reflects the change!) I have tried adding water to both the DT and the sump without effect. My water in my DT is right up to the black trim! As soon as I add water to sump it goes into DT. I bought the stuff for a ball valve on return line, but I keep reading that pump will try working harder and may burn out? I have read about gate vale either on return or drainage, but there seems to be debate with this to? I welcome any feedback that any of you may have. I would really like to add my anxious fish and stock to their upgraded home! Sorry this was so long, but I tried to give you the info you all would ask. LOL:)