The siphon tube you refer to is most likely a short piece of 1/2 inch clear poly tubing about 18 inches long. It may have a 1/2" threaded pvc fitting on one end that is threaded to a matching fitting on you water panel. If no water panel then there is most likely a fitting somewhere in the plumbing area that can be accessed. The open end is placed in the gallon jug and when the winterizing valve is opened and the pump turned on then the antifreeze is drawn into the system. At least that is how my last motorhome was winterized using the siphon tube that was included with my coach. Made winterizing a quick and easy process using about 2 gallons of antifreeze.
With my new Quantum I have to pour the antifreeze into the fresh water tank and then turn on the pump to distribute it to all the fixtures and tankless water heater.
I posted a thread on this earlier today looking for an alternative.
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