You should have two more valves back to the right to direct the inlet from the water pump to the city connection where you now have your short hose. You have already switched the other two main valves. This will also bypass the water filter which you should remove if you haven't. It will take a couple minutes or longer to pull a vacuum and you must have an air tight connection at the hose fitting.
simplest way is to put the antifreeze in the water tank or make up a bucket with a bottom or side fitting with which you can provide a flooded suction to the pump
You will need around 5 gallons give or take and don't let the jugs suck dry, best deal is to use a 5 gallon bucket then you don't have to start and stop
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