For the last twelve years, I filled my ballast tank at the start of the season when I launched. Since this was fresh water, I put 1/2 gallon of bleach in the tank to kill anything live that came in. It stayed that way for 6 months until I pulled out.
Now that I'm trailer sailing, I plan to follow the drying times when I pull out of infested fresh waters. Again, here is an interactive web site to determine the drying time needed based on the time of year and location.
http://www.100thmeridian.org/Emersion.asp
The campaign slogan is CLEAN, DRAIN, DRY where DRY = quarantine time.