RV antifreeze is propylene glycol. It is used in our food, and my favorite, it is used to keep cigars at the correct moisture level. Putting it in the sewer shouldn't be a problem. Since it is used in the food system we are all putting some into the sewer by default.
2008 Chevy Silverado 2500 Duramax Crewcab
Jeep Commander - sold
Flagstaff V-Lite WRB26