So, I am on their web site and looking at image 6 of 8 (Prime Time Manufacturing, Manufacturers of travel trailers and fifth wheels
) and I see the city water connection but no gravity fill port.
I assume that one of the valves switches the pressure from "direct to plumbing" to "direct to water tank."
Is the small round "hole" to the right of the black circle the vent?
If that is how your system works, you can use the same method I use to add sanitizer (1/2 cup of bleach in my case - 40 gallon water tank) to the hose prior to connecting it to the camper. When you turn on the water, it will push the bleach into the tank and plumbing; diluting it to the correct level as the tank and lines fill.
Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW