The suction line is for winterizing or sanitizing - it allows the water pump to suck from an external container, e.g. antifreeze or a bleach solution.
Not sure what the push/pull handle is supposed to do - haven't seen that on a National RV product before. Maybe an owner modification?
I was trying to read the instructions in the photo, but it seems to refer to an unlabeled valve. The PM or FM valve? Can't quite read the letters.
Maybe somebody in the National RV Owners Forum has one like this. Or knows what it should look like.
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL