The forward hookup is for the main black and gray water tanks. The rear hookup is just for the gray tank for the outside kitchen. There is a gray valve handle for the forward gray tank forward of the drain under the slide I believe. (I agree, it's in a bad place.) Its kind of hidden. If I had access to my TT right now I'd take a picture.
2017 Silverado 2500 HD, 6.6 Duramax
2018 Eagle HT 314 BHDS
Blue Ox WDH