Jeremy,
Well I have modified the manifold since the photos and need to update the file. I had the same issue of water in the UDC that I did not like when disconnecting. Our unit is at the shop having a couple warranty items taken care of. When it gets back I'll do some pictures of the modifications. I use two diffierent style of quick disconnects. Most of them came from Lowe's, but I have one set with a built in check valve used on the "black tank" flush to prevent back flow.
What I've done basically is to take a brass "Y" hose connector w/valves and use it as my first connection at the park's city connection. Next on one leg I put the water regulator, then a hose quick disonnect. I carry a couple "5" foot, a "10" foot, and a "20" foot water hose all with matching quick disconnects. Dropping out of the UDC from the trailer is a hose with a quick disconnect (keep a plug on the line when traveling to keep dirt out of the line). I have a stand for the water filter and quick disconnects on both sides of the filter. When I break camp popping the quick disconnect between the filter and the trailer lets the lines drain outside of the UDC. After some comments and conerns that I could contaminate the system with the original hookup for the black flush. I acutally cut that connection which gave a little more room in the UDC. The other side of my "Y" connection from the park city water is setup with a quick disconnect different from the fresh water so they can not be crossed and the first quick disconnect on this line has a built in flow check. I cannot remember where I found this quick disconnect, but it was not Lowe's. I carry a seperate hose for the flush with matching quick disconnects.
Right now, I only hookup the flush line when breaking camp. The think I like most is the ability to have a sealed UDC when camping as opposed to just a 6" hole in the bottom of the UDC for air, bugs, or other creatures to find their way into the trailer. My plate in the UDC stays in all the time and has a seal on the bottom. I built it with the thought that I'd only take it out when the trailer is winterized. When traveling the hose (approx. 3 ft) that drops down for the connection to the filter has a plug/quick disconnect installed and is held up against the frame with a spring broom clamp.
I'll do some pictures when the trailer comes back from the shop in a couple weeks. The quick disconnects, "Y" connector, valving and time spent planning on hose sizes to carry has really simplified setup/brake down.