This is what I've been doing for over 20 years...
1. Drain all of the water out of the water tank and drain the hot water heater.
2. Turn on faucets until all water is out of the lines using the water tank pump until the water "spits' intermittently. You have to be careful as the water pump uses the water to keep it cooled so you can't pump for an extended length of time.
3. Attach adapter to the water hose connection to blow out the water lines with air.
4. Have an assistant keep the air on the system and open the fixture furthest from the water tank. When that line is empty and only air is coming out, open the remainder of the fixtures working back towards the tank location. Blow out all of the faucets / toilet / shower until only air comes out of the fixtures.
5. Leave fixtures "open."
6. Pour RV antifreeze into drains so they don't freeze.
If you want to put RV antifreeze into the waterlines in the water system, you can do that. However, I have found it unecessary if you're careful to get all of the water out of the fixtures and leave them open. This includes the flush lever on the toilet - I keep it open with a bungee.
The problem with antifreeze in the water system is that if you get it into the hot water heater you will have to thoroughly flush the hot water heater before use. If you don't....well, let's say the odor from the heated antifreeze has to be experienced to be fully understood.
The best way to put antifreeze into the system is to have a bypass valve at the water pump between the water tank and the pump. In one valve orientation the inlet side of the pump should be pumping water from the tank. In the second orientation, there should be a short pickup tube you can put into a gallon of RV antifreeze. This will put antifreeze into the water lines between the pump and the water fixtures.
Open the furthest fixture from the pump first until antifreeze comes out, repeat with the remainder of the fixtures including the toilet.
To drain out the antifreeze - repeat the same thing you did with the antifreeze at the pump -only using water. This will force out the antifreeze, including what is in the pump.
Connect a hose to the water inlet and run more water through the system. If you want to use the water tank, fill the tank and put in water tank freshner.