Use this Submersible Velocity Pump when you need to drain large swimming pools, fish ponds or lakes. It connects to a hose, so you can position it where you need it. It pumps small debris without clogging and continues to operate in wet or dirty water. The pocket-sized is suitbale for industrial and domestic, drains water at same rates. The venturi effect occurs when liquid flows through a compressed section pipe. It increased fluid velocity and reduced fluid pressure.