That's an easy one, the tank under the cowling has a level switch on it so it automaticaly gets refilled when at low end. There is additional common circuitry involved too, one of the other members will respond hopefully with some troubleshooting info. If he's not a DIYer, get it off to the dealer.
If he unplugs the connector going to the boat's tank, and monitors usage in motor tank until it gets fixed, he can probably use the boat. If he doesn't moinitor usage though, bring check made out for $5 for new powerhead when going out.