[DutchmenSport]

That is the check-valve for your black tank flusher. You attach a garden hose to your black tank flusher in your convenience center and turn shore water spigot on. Water flow through a separate water line (the white line). It will travel through that pipe under your sink. That black "thing" is a check valve, which allows water to flow only one direction. This way, there is never any back-feed from the black tank that could feed backwards from the black tank BACK into the garden hose or worse, back into the campground (or your hosue) water system.

It is important to have that check valve in place, but sometimes when they fail, folks will remove them completely (not a good idea though). Others will be a little beefier model, like the one pictured above in the prior post.

But, that is what the white pipes and and black "thing" connected to them is.

The only time you'll have water in that line is when you flush your black tank via the black tank flush hook-up in your convenience center. And yes ... when you winterize, you do need to either run some RV pink stuff antifreeze through that line, or at best, blow it out. It does hold water and it will freeze up and break if not winterized, just like the rest of your water lines.

Happy camping!