I looked at it this way: one of those valves is nothing but gray water, and you only need the giant hose for black water. The giant hose is awkward, so why deal with two?
I outfitted the gray-only valve with
a bayonet cap that had the additional garden hose connector, and got myself a
red gray-water hose for that valve.
Then I bought a new Prest-o-fit blue elbow (an item which I've used for years and swear by) and a male bulkhead garden hose fitting (image). I ported the elbow on the side (where it's a bit off the ground no matter what side of the elbow is down) and installed the hose fitting. (I had to caulk the inside, as the inside surface is a tad Escher).
When I overnight and won't be dumping the forward gray tank, I cap the hose fitting with a brass hose cap. When I am staying for a while and want to hook everything up, I put a female-female hose connector on the elbow and run the red hose to it.