Shower in a Can is a light blue spray can. The label on it is light yellow with a shower head above the title and the product's name is written in red. It is operated like a normal spray can and resembles deodorant.
Role in episode
Mrs. Puff uses this spray on SpongeBob after he stays up all night, studying for his field trip. SpongeBob is dirty/smelly and missing his teeth. As a result, Shower in a Can cleans him up instantly.
Apparently, Mrs. Puff carries around a bottle of this spray.
When Mrs. Puff is spraying the Shower in a Can bottle, her fin resembles a human hand with an index finger and thumb.