As all have stated , open the black tank valve. I usually dump first, and flush 2nd. In that order works for my TT. A cheapo water hose works just fine, most campgrounds in my area have the hose "they provide" hooked up to dump station water spigot. When I get home I spray my bleach/water mixture on the inlet spigot.
So the dump lasts about 5 - 9 minutes, and I flush 10 minutes usually.
Another thing too, I placed a decal near the black tank rinse spigot so as not to confuse it with the city water valve, mine are close to each other.
Go to a local campground or if you have a sewer connection on your property, practice in the daylight.