RV Repair: one way water valve, valve question, lowe s

Question
QUESTION: Where is the location of the oneway valve on the city water line on a 2009.  21 foot terry classic cruiser

ANSWER: most likely it is near the pump outlet

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QUESTION: Will this be easy enough to do myself versus taking the trailer in.can you give me an idea on how to get at this. I understand it can be hard to get at

Answer
what is the problem with the water flow?  Is there an issue where your city water hose is filling your holding tank when turned on?  or is there a problem with not keeping prime when pumped water is off?  Is there a problem at a particular sink?

The one way valve can be part of the outlet of the pump.  It can be located before the pump also, but usually not.  It will usually not be located any further in the system than where the pumped water from tank and city water from hose come together at a "T" in the tubing.   

If the pump and water lines can be accessed easily, usually in a closet behind a false wall, then the repair can be easy.  Home Depot or Lowe's will have things to fix this and the price might be cheaper.  People there will walk you though how to install parts in the tubing.  

It is also an option to have manual valves you can open and shut by hand to assure there is no backflow where you don't want it.