Sounds like you have bacteria in the line from the tank, through the pump, and on into the main water system. The way to remove it is a shot of chlorine. If it is in fact only in the lines after the fresh water tank make a several gallon 10% chlorine patch and put it on the fresh water tank. Draw that up through the pump and into the water system till you smell the chlorine at each of the taps. Let it set a 1/2 hour. Draw a quart or so from each tap and let it set again.
Fell the tank to use the remaining chlorine to serlize the tank. Drain and flush the system with fresh water till chlorine smell is gone.
If you have any reason to believe the problem is in the piping from the city connection to the tank attach a 25 ft hose to the trailer water connection, raise the hose above the connection and pour chlorine into the hose to fill the hose. Now attach the hose to a faucet and force the chlorine into the trailer. Let that set as above and flush thoroughly.
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles