Use once as a free action: choose an empty square on your back rank. Enemy pieces cannot end a move there for your opponent's next 2 turns.
You draft Closed for Cleaning in either mode. Free action: you choose when to use it, and it resolves without costing your turn.
As a item card, it is a one-use consumable, drafted in either mode.
“The mop bucket outranks the cavalry for two turns.”