Do not put any antifreeze into your fresh water tank, but do be sure to drain it completely of water. You should have a water heater bypass so that you don't put antifreeze in there, either. Remove the anode/drain plug and drain the water. You can use a small piece of tubing to siphon any remaining water or just stuff a clean rag in the opening enough to get it wet and let gravity drain it. Then loosely insert the plug back in to keep critters out. Pour some additional antifreeze into each sink drain and into the black tank, via the toilet. Then put some in the toilet bowl.
I prefer to first evacuate the plumbing in my rig by using air pressure (40 psi) via the city water inlet, then pumping antifreeze via the water pump siphon at the UDC. Takes almost 3 gallons for my 3670, with the washer/dryer. I also have low point drains on my rig, so I can get all of the water out.
In the spring, I'll use air pressure again to remove the antifreeze and then run several gallons of lightly chlorinated water through the plumbing via the water pump siphon to clear the lines of antifreeze. Once at the campsite, I'll run city water through everything for several minutes. I also have to run a cycle (empty) on the washer to clear the antifreeze from it.
Sounds like a lot of work, but it's really not. Winterizing might take me an hour (I'm slow) and dewinterizing about the same.