Note: This post was moved from a parallel thread.
So...this is similar to your post in another spot - might want to just post in one spot. I posted a reply there. With my 2501ss, the low point drains are on the door side in the rear below the bathroom sink area. These are used to drain out most of the water prior to winterization. For using the connection to city water, they have no connection. When you attach your fresh water hose from the spigot to the city water connection on the trailer, the pressure opens a check valve that then shuts of water coming from the water pump supply (don't need water pump on when hooked to city water) and allows the city water to flow through the system. If you are using the fresh water tank on the trailer, there of course is a separate fill for that and its own drain valve that is usually located somewhere below the fill. Hope that helps.
Pull-Rite 16K Super 5th
2014 Rockwood Signature Ultra-Lite 8289WS
2011 Chevy 2500HD - DuraMax (Just over 5000 miles now!)
Nights camped in 2014 - 21