What is the purpose of the little hole that leaks water on the side of my rotor's stem?

It's a combination drain hole and flush hole.

It's a drain hole because we need to drain the water from below the nozzle turret so it doesn't push up on the nozzle turret in freezing climates.

It’s a flush hole because when the head retracts, water and is flushed out of the hole, forcing debris from the area below the nozzle turret.

Note: Clear model used for demostration purposes.