[JRTJH]

First use compressed air to blow out the black tank flush system, Then think about the following:

When you turn on the hot or cold water faucet at the outside shower, it will run whatever is in the lines out of that faucet. So, when you're pumping antifreeze through thte cold and hot water lines inside the RV and then to each of the faucets, as you turn on the outside faucet, it will flow pink. If you plug in the hose, adapt it to a 3/4" male garden hose fitting, you can screw it into the female black tank flush fitting and pump "pink stuff" into the black tank flush system. You won't be able to tell if you've filled the entire flush system line unless you open the black tank valve and observe pink flowing out of the tank. Then you can be assured that the anti-siphon valve is protected.

I find that using a hand pump is much easier and faster, however I always ALWAYS use air to blow all the water out of the line beforehand. That way, there's no doubt when I hear liquid flowing into the black tank, it's antifreeze.