There should be one.
While my unit is a little different my overflow tube is right next to the fresh water drain tube.
Curb side just behind the back axle about a foot in from the wall.
It is white with no cap or valve.
2016 F350 6.7L LB CC Reese 28K 2014 Chaparral Lite 266sab
"Those who would give up essential Liberty, to purchase a little temporary Safety, deserve neither Liberty nor Safety." 2014 19 days camping 2015 17 days camping201620 days camping