A self-contained water pump - photo below. Using three good quality alkaline batteries it will pump 757 litres/200 gallons per hour for up to 5 hours. Has a small enough diameter to fit down the BayRaider ballast tank hatch.
Specifications:
Comes Complete with 42" Hose
Completely Submersible
Weighs 2lbs
6 3/8" High x 5 1/4" Diameter
Barely used and cost about £50 new - will accept £20 ono. I have changed to a higher capacity 12V Rule pump.
If you are interested, contact me by pm or (less reliably) by email: graham dot wickenden at btopenworld dot com.