Originally Posted by 73shark
What purpose does pouring antifreeze down the drains serve? There are no P-traps.
The black tank and gray tank are never completely empty even after dumping, so pouring antifreeze down ONE drain and the toilet gets antifreeze into the waste tanks. But since the antifreeze is diluted by whatever was left over in the tank, it can be less effective. The final pre-winterization black and gray tank dump will be more effective if you elevate the passenger side of the van before and during dumping.
Fair warning, RV antifreeze mixed with some black tank treatments can form a thick, viscous goop (with a consistency similar to snot, ew!) that will not do your macerator pump any favors. Strongly advise flushing the black tank thoroughly
to remove any trace of black tank treatment before adding antifreeze.