[DutchmenSport]

You can put an RV flush valve prop into the hole of the toilet, which will hold the bottom of the toilet (slide) open and allow water to run without having to hold your foot on the peddle. When the water reaches the bottom of the neck of the toilet, then pull the prop out of the hole and flush out the tank.

Before the days of black tank flushers, this is how I filled my black tank. It works, easy, and no mess.