We have the same setup. When we got the TT new, we bought a Valterra wye fitting. Used it exactly once. I simply drain the forward black/grey tanks and then move the hose to the rear kitchen grey tank outlet. Easy peasy, lemon squeezy as they say. Want a wye? Make us an offer we can't refuse. *Almost* like new. :)
The thing that is a nuisance is that in their infinite wisdom, the factory put the forward outlet partly under the slide so I have to kneel down on the ground to attach the hose when the slide is out. Pffft... :M