Yes, it is for winterizing. I have the Freedom Elite version of the same coach. At our PDI I speculated that was the purpose but the camping world fellow assured me it was not (although he did not know what it WAS for?!). In an unrelated communication with the helpful people at Thor I asked and they said it was indeed for winterizing - to suck antifreeze directly from a bottle. So this spring when I was de-winterizing I tried it. I sucked water from a milk bottle and it worked a treat. Surprisingly, there is just the one valve - you don't need to first isolate the tank. Perhaps that is why the connection is higher than the tank so that gravity can assist. It was a pleasant surprise to me to find this feature on a budget/entry level coach!