Sink plumbing drops down to the space under the waste basket (or water heater in non-HHot units), where it lands in a short 90 in the far back outside rear corner of the slide, just above the slide floor. From the 90, WRV ran "spa" pipe, a not very but somewhat flexible PVC pipe, through a long sweep to exit the slide. The long sweep is all there is to allow flex in the waste plumbing as it exits the slide.
If you lift the bottom of the black rubber flap between the slide and the stationary "pantry" doors that get covered when the slide is in, you will see the end of the spa pipe where it enters a short 90 ABS fitting that drops thru the coach floor to the basement. There is a black rubber diameter change fitting over the spa tubing and over the outside diameter of the 90, with hose clamps on both ends.
You can probably trim the bottom 8" or so of black rubber sheet off the slide "trim" flap and lose nothing to aestehtics, while gaining good view of this fitting when you go looking for it.
On mine, the spa piping was getting pinched by the slide closure action (and by the slide opening action at the other extreme). The hose clamp fitting & the spa piping inside pulled loose from the 90 thru the floor. Water leaked onto the Xantrex in accordance with gravity, which happened to be operational that day.
I pulled out the drawers & HHot radiator that faces the fridge (didn't disconnect it, just unfastened it & pried it up a bit out of the way), pulled the thin panel lower left of sink cabinet, all to get access to the spa piping. I removed ~24" of the spa piping and replaced with same outside diameter tubing, same length (exact length seemed important to operation without unnecessarily pulling on the fittings). Replacement tubing (looks like this stuff
, and comes on a roll so you buy however much you need) is much more flexible swimming pool vacuum tube, ~2"o.d. iirc, but it is spiral exterior; so I filled the spiral gaps w/ 3M-5200 far enough back to exceed the fitting req'mts on each end. I used a straight coupler on the spa tubing splice end, and a new bell joint w/new hose clamps on the other. All parts from H.D. or Lowes except the 5300 which I got from West Marine near me.
Project takes a while as its a beeyatch to get to even on the older models. I repaired Figge's 02 when theirs gave out at the Paso Robles rally last year using same method; the earlier coaches have way better access as you can disassemble some of the cabinetry to actually get in close w/real tools. I had to cut the spa tubing on mine blind, using the saw blade on my Leatherman as access was so tight and anything longer wouldn't get at the pipe and still have room for a sawing stroke.
Here are the parts (I tried silicone sealer in this photo which easily pulled loose and would have leaked, hence the leap to the much better 5200):
On reassembly, I recommend zip tying some "cutting sheets" between the waste piping and other bundled stuff that has to slide/bend when operating the slide. It helps for the odd parts to be able to slide a bit against each other as the bundle of wires, tubing, and hoses flexes. One cutting sheet on the bottom of the whole bundle helps also so the bundle slides easily on the bottom "platform" WRV built up for this spaghetti to rest on.
If you assemble the parts & tools, thereafter you're looking at 4-6 hours for this project depending on coach obstructions.
There is another more drastic problem that may have occurred, that being the 90 degree fitting thru floor may have broken. If that has happened, there will be more major surgery including some serious work under the floor in the ceiling area of the utility bay.