I just did my 24 E Pro 15TB, super easy.
Drain your hot water tank
Open your low point drains, Open the all the faucets also then shut them and close the low point drains once done
Close off water heater valve and move valve on water pump to only antifreeze will now pump from outside. There are 2 valves to close off, hot and cold valves.
Open antifreeze inlet outside, it is on the opposite side of your city water inlet
I made a short piece of hose to screw onto the antifreeze inlet and had the tube go to the bottom of the antifreeze jug.
Now go in turn on pump then turn on each faucet hot and cold until pink stuff comes out then shut off, then do the same with the shower hot and cold, keep the miser off.
Next flush your toilet until pink stuff comes out, I let some go into the black tank and leave some in the bowl to cover the seal.
Go outside and hook up your shower and do the same for hot and cold, I use a bucket to spray into. Turn off once you see pink stuff. I then take that bucket and dump into the sink drain.
I pour a little in the sink drain also for the gray tank, your shower will also get some going into the gray tank. Seeing we have wet baths, I take the shower head out of the holder and point it down at the floor so I do not get the entire area covered in antifreeze.
Your done. I used 1 gallon for the full process. Then I used a little out of the second gallon to pour directly into the sink and toilet. Total job 1 1/4 gallons.
Obviously make sure your black and gray tanks were already empty and drain your fresh water tank also. If you used your shower miser by accident then use a bucket to catch that antifreeze that comes out.
Hope this helps.