Welcome to the forum
I can’t say where the hook up,is but if you have a convince center it’s probably located there.
How it works is you hook up your hose, NOT YOUR DRINKING WATER HOSE, to the port on the trailer, turn on the water and open the black tank drain valve. You should see a warning sticker very near the rinser port that says not to use it unless the valve is open. You can close the valve just DO NOT leave it unattended. The more liquid you can put in the tank, the better the flush and the more the solids will come out. You can repeat as many times as needed to see clean clear water. Most use a see through piece connected to the trailer and then the hose connected to it.
2012 Copper Canyon 273FWRET being towed by a 1994 Ford F350 CC,LB,Dually diesel.
Airlift 5000 bags, Prodigy brake control, 5 gauges on the pillar.Used to tow a '97 Jayco 323RKS.
Now an RVIA registered tech. Retired from Law enforcement in 2008 after 25+ yrs.