Pool Cleaners are Lawn Mowers for pool lanes. They can be purchased from Crazy Dave in Crazy Dave's Twiddydinkies for $1000. Otherwise, regular Lawn Mowers only stop zombies that are out of the pool, as they sink once they fall into the water. When a zombie tries to exit the pool to enter the player's house, the Pool Cleaner will activate and suck all the zombies in the lane down the funnel sticking out of the water.
If the player looks closely, they can actually see that this item swallows zombies.