Welcome to the forum. As you can see, many here are willing to share their knowledge and experience with all who ask. There are no stupid questions here. The only way to learn is to ask so don't hesitate any time you need info. I generally don't leave my sewer hoses attached. I attach, dump, then disconnect and rinse and put them away until the next dump. Too many times I have heard stories about damage occurring to hoses by critters, kids cutting thru your site, being stolen or other B.S. I don't find it that much trouble.
No damage will occur if you close the valve while your rinsing, just don't walk away and forget it. That's when the bad things happen. As stated before, use a dedicated hose for your rinse and a drinking water approved hose for your city water hook up. I use a "y" on the spigot with an anti siphon breaker on my utility (rinser and general out side water use) hose. Anti siphon breakers are important and most campgrounds have them on their spigots. If you do a Y on your water hook up like I do, be sure use a breaker on the side of the Y you use to rinse too. Here's the sequence, CG spigot with Anti siphon breaker, Y, one side hose to city water connection on trailer, other side of the Y, breaker and hose to rinser (which you don't need to leave connected, use only when you rinse) I put a spray nozzle on that hose when not used for the rinser.
