In relation to filling the wheels, simply unscrew the valve and fill via the tap after which replacing the valve. You can establish the quantity by competely filling it first then poaring it back into a measuring jug then using only 40%....Pirate
If you're going to put water in your tires, here's a couple of tricks from the farmers.
1. After removing the valve stem insert, why not just drop the tire in a bucket and let the water flow in?
2. To end up with the correct amount of water, have the wheels on the frame, the tires off the ground, rotate the tires to prescribed position and let excess water run out of the empty valve stem. For small tractors, I usually fill to the top of the hub position. Amazingly, any excess always drains right back out. To get 40%, try rotating your tires so the valve stem is at mid hub. When the water stops draining put the valve in the stem and a couple of puffs of air and you're ready to go. Be careful not to overinflate! When airing and checking pressure the valve should be up higher than the water level. This method is quicker and more accurate than filling up the tire and then pouring some out.
3. Be sure any water additives are non toxic for when it leaks out later. Since there is nothing in the wheel to rust, I agree with Stringy that antifreeze shouldn't be necessary since the air chamber provides expansion room.