Either Streifeneder or DG-Flugzeugbau can probably help you with the bags and valves.

When I was designing the dump system for the HP-24, I couldn't find anything commercially available, so I ended up making my own valves from commercially available components. I considered several suppliers for the bags before going with Streifeneder. The price was reasonable, and the bags were good quality and matched the drawings exactly.

Just curious, are there dump ports in the bottom of the wing? Or does the system dump through the fuselage?

--Bob K.