Hi Kurt,
Let's assume you've resolved your water ingress problem and turn to fuel polishing.
Remember that your engines are probably the best polishing systems and are already on board. Excess fuel drawn by the engine fuel pumps will have already been filtered before being returned to the tanks.
Real polishing is where any water, diesel bug and debris that's settled on the bottom of a tank is removed. This takes knowledgeable pipe installation and powerful pumping to stir everything up before being drawn off, filtered and returned, polished. BTW, a centrifuge filter is by far the best but many use Racor filters.
Hence, the method of piping and pumping is absolutely crucial and something which is often overlooked by the sellers and installers of polishing systems.
To be effective, you want the outflow from the polisher to be powerful and aimed at the bottom of the tank to create a real stir. The draw should be about halfway up the tank.
Given time, all the muck your engines and common polishing systems you can buy cannot reach, will have been polished.
Piers