Originally Posted by wingnut60
Not familiar with Aljos, but every older TT I have had, had a fresh water connection. Find that, find it inside and follow it--going to have some connections/valves in the system somewhere.
Sorry it don't appear you have found an answer.
I looked for photos of 1998 Aljo fifth wheel trailer to see what they used for water hookups. Best I can see is a hose fitting on outside. Did not see any pour type housing to fill you fresh water tank so I assume you are filling tank with the hose hookup. IF so it should have a valve (like you asked about) to direct water to tank or trailer plumbing, as needed. This would normally be close to the inlet fitting of trailer. I see water heater by hose hookup in photos I found. Possibly the valve would be in the access area (cabinet maybe) to the water heater (Heater bypass valves used for winterizing are usually there assuming it is equipped with those valves.)
My answer is not really any more than wingnut60 said.
Photo (IN and Out) may have given us a clue to the type installation used in 1998 on your unit.
Good Luck in your search.