Continuity mistake: When every one in the rough tub bar are told to line up, SpongeBob is standing next to a fish with an eyepatch. When showed from behind the fish is orange but is later dark green.
Factual error: King Neptune's crown changes size when Plankton steals it and when SpongeBob and Patrick retrieve it.
Chosen answer: The buckets don't brainwash through skin contact. They brainwash through Plankton's signal. All you need to do is wear it close to your brain.
MikeH