You must have a very tight connection at the hose. The slightest air leak will prevent the pump from pulling in the antifreeze.
I set the antifreeze jug on a short step ladder at near the height of the hose connection. I do not drain any water. With the hose in the antifreeze jug I turn on the pump, then open a low point drain until antifreeze comes out to get flow started, then close that drain. Repeat with the other low point drain (I have two). Then it is generally good for doing all the faucets, toilet, washer/dryer, black tank flush, and outside shower. On rare occasion it will lose its prime. When it does, I go back and open a low point drain again to re-establish flow and reclose it.
I have the ladder and jug set so I can see it out a window so I can close a faucet if the jug gets low and before it starts sucking air.