Yup i think your right onto something there Razz. I think ill get the first two pictures. The screw in adapter and then the quick release fitting so it looks like the others. Then a T junction and some 3/4 hose and run it from the front of the bag back to the lower drain line. Hopefully that works.

I dont quite understand why only the front bag fills with air. Must be the way that drain port is on the curve of the hull in the front.