Terry:
So both of our suggestions require some additional work. In the case of the S89R that you recommended...

http://www.pandbrelays.com/datasheet...990_DS.pdf

It appears to me that manual operation of the armature would cycle the toggle mechanism back and forth. In other words the filler could push it once and "set" it but another push would "clr" it again. The pin on the armature toggles a plastic rocker back and forth to open and close the side mounted micro switch.

In the case of the device I suggested some additional work needs to be done to detect the in or out position of the plunger. This may be possible with a microswitch but I think it would be much more elegant to excite/monitor the coil somehow to detect plunger position.

Michael Karas