If the FOB is that obviously dirty the rest of the system is probably in dire need of a scrubbing too. The FOBs are easily taken apart by turning the top clear jar off of the base. After you take this off the inside piece at the base snaps out. Once you have opened up the FOB, check to see if you can repair the float or try to determine if the stem is damaged not allowing the float to stop at the base of the stem.
When placing the jar back on the base, simply turn until the "stop" does not allow you to turn anymore.
Scott Zuhse, Instructor
Micro Matic Dispense Institute