I don't think they had sewer connections in 1492??
No need to watch a video.
Know nothing about that unit, but assume more than one outlet/hose connection location and assume manually operated valves. Just connect hose to the outlet that has both black and grey handles to pull. Pull black first, then the grey. Then move hose to the next outlet. If both black and grey, pull black handle first. If just grey, you're almost done. You want the grey water to be the last one to flow through the hose so it helps rinse the contents out. There is a wye fitting available for hoses for multiple outlets - we bought one and only used it once. Easier to raise the end of the hose a bit and "walk" it over to the next one.
Valve handles should be color coded and there's really no need to know what's connected to what. If you look underneath tho., you may or may not be able to see the ABS waste pipes (black color). A 3" is for the black tank and a 1-1/2" is for grey.
For flushing black tanks, fill the tank(s) as full as possible before dumping. Helps flushing the contents out. A clear elbow really helps to see what's coming out. If little bits 'n pieces of "stuff" are still coming out, may need to repeat the process by filling the tank up again. Can take a while but if you want your black tank clean and trouble free, gotta take the time to do it. And use the in-tank rinser (if so equipped) to help clean it.
Tip of the day: Never skimp on water when you flush and add a few gallons before each use of the tank. If you don't, you can get the infamous pyramid of p**p and prematurely need to dump & flush the tank which can be a PITA.