I have a 2004 Designer 5er, and the fresh water fill is a screw cap on the rear, right beside the city water connection. Tank is under the rear of the trailer. Look under the trailer for two short hoses sticking down - these will be the overflow hoses for your FW tank. Nearby should be a valve to drain the FW tank.
2003 Ford F-350 V-10 Crew Cab 4WD Long Bed
2004 Jayco Designer Medallion 29 RLTS 5th wheel
Bill, Gayle, and Mindi (dachshund)
Retired at last !
Nothing is foolproof to a sufficiently talented fool.