Ok, al lot of this is "Generic" but...
The most basic water systems (COLD ONLY, I will do hot later)
Note.. This is not how it is done.. but is effectively how it is done
City water enters via a check valve (part of the inlet) and then goes to one side of a "T" fitting (Reality check, feeds into the water system at the closest point)
Tanked water goes to the pump, which contains a pair of check valves and feeds the other side of the above T fitting (Reality check, same as above)
The water system comes off the "T"
No power to pump
Pump inlet strainer open to air
Tank outlet valve closed
No water in tank
SOME RV's have a "Winterize" line and valve.. This is used to such Pink stuff out of the bottle into the lins for those who choose to waste money and put noxius stuff in their water lines that is hard to rinse out come spring... (I did it once.. after that I used the dry method.. If air freezes I'm not going to worry about the RV's plumbing).
IF yours has this valve it becomes #1 on the suspect list.
Hot water has a bypass system This may be 1, 2 or 3 valves.
1 Vlave has a check valve on the water heater outlet
To bypass put valve in bypass postiion (Usualy pointing toward the watr heater outlet or the bypass label)
To use return to the use position Pointing toward the cold water inlet
2vlaves one on the hot and one on the cold
Bypass they point toward each other
Use toward the tank or 180 degrees from the tank
3 Valve One in cold line, one in hot, one connecting the two
Bypass close hot and cold valves, open bypass
USE.. Open hot and cold, close bypass
Do not forget the water heater drain plug.
Home is where I park it!