The two overflow tubes go straight down through a hole in the floor and both come out under the rear of the coach right next to the trailer hitch. You can clearly see the ends of both of them. The lines coming off of the fill valve are a little trickier. There seem to be two lines- one of which is the aforementioned line going back to the pump- which run through the back wall of the holding tank bay but they must run through the "subfloor" of the coach if there is such a thing because they are not visible from underneath the coach. From the direction it runs I am going to guess it is going to the hot water tank.
BTW in case it matters the HW tank is full (we cracked open the drain out and got both water and pressure) but I can't find any way to access the other side of the HW system where it's fill line would be
