Allow the sight tube to show column (an inch or more) of antifreeze. After this go into the PUP and flush the toilet until 100% pink, undiluted, antifreeze is flowing into the toilet (Not shown)
Unlock and open the cassette toilet door and locate the clear plastic sight tube for your freshwater supply to the toilet (seen on the right). As shown here the toilet fresh water tank should have antifreeze in it. This has to be drained out.