Drain Valves

[SnP Farm]

Just purchased a 2018 Forest River Heritage Glen Hyper Lite Bar 337 5th wheel. Presently On our first trip with this camper. We've had travel trailers in the past. This is this first with 2 grey tanks and 1 black tank. All 3 valve handles are grey. Which of the 3 is for the black water tank? There is no markings to indicate which is which.
Thanks,
Scott and Paige

[lcv800]

One sure way is to drain all 3 tanks then close all valves, then flush or run a hose to the toilet for a few minutes. Open and close valves one at a time until you find one that drains. Do the same with each sink, shower, washer, etc. one at a time and you'll find out what goes where. There may be other ways, but this way you'll know for sure.
Rusty

[SnP Farm]

Figured it out by luck of the draw. Of the three valves the black water drain valve is closest to the rear.