It really doesn't make much difference, Joe. Leave 'em open if you'd like I guess! I leave mine closed when filled with pink.
Chris, you can blow it out if you want, but its really easier just to flush it with fresh water in the spring on your first camping excursion. The anti-freeze really doesn't have a taste. I winterized the Big Bigfoot
last week 'cause we had some sub-freezing temps, and then we used it Weds thru this morning. I just flushed the lines out with fresh water after filling the tank, and we were good to go. I dumped the tanks this morning, and let the fresh water tank and water heater drain themselves out. I'll re-winterize with pink antifreeze after work tonight.