www.thetford.com click on Parts at top selecting permanent toilets on dropdown menu.
Your's middle picture 3 one down C-200 click on that and up comes the exploded view of the toilet and scroll down and the parts list named and numbered parts. I am sure our dealer/service engineer said the electric valve is in the bottom of the water tank and is accessed through the top of the tank after removal of the switch. Lift the tube out and valve is on the end.
Bob
September 2008