Can't speak specifically to the Jayco unit, but there sometimes are. My Salem Hemisphere has a drain immediately below the fresh water tank with a quarter turn petcock on it, but many don't. You don't indicate which model you have, but here's
a link to the owner's manual for 2003 Granite Ridge. It has sanitization procedures that should show their recommended way to drain the tank.
2018 Forrest River Salem Hemisphere 282RK - 2017 RAM 1500 TV
Previous RVs and TOADS
2004 Fleetwood Bounder 32W on WH W20
2000 Four Winds 5000 21RB
1986 27' Allegro
TOADS
2005 Ford Ranger XLT 2WD
2004 Suzuki Aerio
1988 Chevrolet Sprint