Reverso Diesel Fuel "Polishing" System

A solenoid valve with its power supplied by the power going to the motor should be a simple solution that old conundrum.

I know fuel polishing is the hot new sales pitch. I suppose for people that use their boat mostly at the dock it may not be a completely waste of money.
I'm almost 68 and have been running marine diesels since before becoming a teen. Over that time I have returned to service many boats/ships/engines that sat for years and some for decades. Using nothing more than a quality fuel conditioner, primary filters, and an auxiliary fuel pump.
My current boat, an 83' 1942 Wheeler, sat for 6 years before I bought it. It has 1942 steel tanks, each about 5-10% full. I added Algae-x, a magnet in the main fuel line(to catch rust particles) and circulated the fuel thru the existing Racor filters. Two years later, when I remodeled an area that allowed access to the tank tops, I went inside the three main tanks. The tanks were clean, no water, no bio growth, only a little rust debris. In that time I had made ocean passages in the PNW, Gulf of Alaska, some in gale conditions. Other than the original filters, I have yet to have a clogged filter problem. I currently run 2 micron filters in the Racors without problems. My mains pump 70-80 gallons/hour and return all but 10. So the fuel is filtered many times before consumption. I buy my fuel from commercial docks.

What J said. And in rather more developing countries, the quality of fuel storage shoreside is often not of US/Can standards.

Pardon my language, but to quote my late father, full of rat's piss.

Polishing wasn't important when we were in the area Lepke boats. For a boat just cruising the US coast probably not necessary. But, for the Bahamas, Caribbean, and Central America we've been glad we had it.

We're doing the loop and you'd think not important. Well, think of all the marinas on the Erie Canal, closed for months, opening up on May 1. Along our way we talked to people from two different boats who had filled at two different marinas and had problems. A local fuel company came to the dock with polishing equipment to help them. One had sputtered in and the other towed in to the same marina, up the canal from where they fueled. We fueled before leaving NYC area so we could make it as far without fueling again as possible. We paid the extra to fuel at a year round marina on the NJ side of the harbor.