I don’t put antifreeze in my tank. If that last little bit does freeze, it’s not gonna hurt anything because there is plenty of room for it to expand.
As for pushing antifreeze through the plumbing I can’t recommend this piece enough. It is a valve that installs between the tank and the pump, lets you switch between the freshwater tank or a hose leading to a jug of antifreeze as your source for the pump. It makes real winterizing a snap. I can push the pink stuff through every faucet with a single jug of antifreeze and then use a second jug to dump down the drains for P-traps etc.
https://a.co/d/1LQJNpf
Of course you’ll also want to use a water heater bypass or else you’ll need an additional six gallons of antifreeze to fill the water heater tank before it will push through the hot water faucets.
https://a.co/d/j5qnB5p
Anyway. As for the question of getting every little bit of water out of the tank why not put a small hose done the fill tube and suck it out with a shop vac?