Question: where can I find the place to add my water/bleach mixture to sanitize the water lines in a 1998 gulfstream yellowstone fifth wheel?
Answer: You may have what is called a gravity fill opening. This is typically near the hose connection for the city water, often a larger opening so that you can pour in bleach in addition to filling it with water.
You may want to contact Gulfstream to see if you can get an owners manual for your RV, or ask them for instructions on sanitizing the water system for your specific configuration.
From the general owners manual we found online, it states that “Some models have a separate water fill for the FRESH WATER TANK. Others have a selector switch to select either LOCAL SUPPLY or FRESH WATER TANK. To use CITY WATER make sure the selector is set to LOCAL SUPPLY. The fresh water tank and water pump are by-passed when the city water hook-up is used.” So if you have a selector switch, you may need to set it to Fresh Water Tank while you are filling the tank.
We found that general owners manual at: http://gulfstreamrvtrailers.com/media/pdf/gulf-stream-owners-manual.pdf.
But you may want to call them to make sure you have the most accurate material for you model year fifth wheel. See http://gulfstreamrvtrailers.com/contact-gulfstream.php.