you don't need valves what you need is a syphon break valves installed. I'm surprised builder did not install them unless they are stuck and not working. Purpose of a syphon valve is so when your tank is full to the point where water comes out the overflow it doesn't just keep coming out and emptying the tank. My first RV had the same problem no syphon valve so in a pinch I drilled a 1/16 hole in the top point of the overflow hose until I had the opportunity to install the proper valve.
you don't need valves what you need is a syphon break valves installed. I'm surprised builder did not install them unless they are stuck and not working. Purpose of a syphon valve is so when your tank is full to the point where water comes out the overflow it doesn't just keep coming out and emptying the tank. My first RV had the same problem no syphon valve so in a pinch I drilled a 1/16 hole in the top point of the overflow hose until I had the opportunity to install the proper valve.
The manufactures do need to set these up better.
Your "buddy" must be a genius to have his trailer already equipped with valves.....or he bought it that way.
It's lucky that my buddies trailer was that way when he bought it. I do't know if I would have know how easy it was to solve.
Trailers are made junk from the factory
The quality seams to go down every year.