Is there any reason NOT to use Prestone car antifreeze in the drains leading up to and including either black or grey tank?
None that I can think of.
You would want to recover as much of the auto antifreeze as possible as the Ethylene Glycol is a hazardous waste. Wouldn't want it in a septic tank.
You will not be saving much money, highly toxic like crane man said.
It's not legal to pour automotive antifreeze down a drain, or on to the ground where it can contaminate ground water. it is very toxic to septic systems which are often found in campgrounds and state parks, basically not a good choice.
Stick with the PINK!
Pink it was!