My pop-up had the same arraignment. I just used normal clear water for the flush water (yellow arrow), the red is your flush water level gauge (to drain your flush tank, you pull the clear tube DOWN and out so the water drains away from the camper body).
Use the funnel the blue arrow points to so you can fill the flush tank, water will be visible in the fill tube.
For your cassette tank, I put enough water to cover the bottom, and throw in a tank deodorizing pack to keep odors at bay.
To drain the cassette, you can either use the dump station at the campground or a toilet. I used a sewer hose placed over the tube, pressed the little green button, and dumped it out, thought the hose into the dump station's drain. Works really well.
"Do or do not, there is no try" - Yoda
"Do, or do not, there is no try." - Yoda
2017 Cherokee 294BH
2015 Ram 2500 4x4 6.4L V8 Crew Cab