Dan, If you pull the boat out of the water I
would drain the ballast tank right at the boat ramp before towing the boat. Both salt and fresh water in the ballast tank would benefit from 3/4 to 1 gallon of bleach to prevent growth and smell in the ballast tank water.As far as I know, leaving the water in the tank that long is not a problem. Changing the water every 4 to 6 months would not hurt a thing, but I don't know that it would help either.The water can be changed in the boat, while it is floating next to the dock, by opening the bottom water ballast tank valve and using a hose with nozzle, in the air vent hole, next to the tank top large wingnut. This flushes out the old and fills with new water. If you want the extra weight of salt water you will have to find a salt water supply line somewhere near. RayS/v Speedy95 H26