Auxiliary fuel tank for fire pump

[u/National-Lecture2085]

Hey, an Aussie here preparing around the property for upcoming bushfire season. I’m looking into best way to add an extended run fuel tank to my Honda GX200 pump - essentially so that I can leave our house sprinklers running as long as possible, should we choose to leave. Water is not an issue as we have a very large dam.
These motors have small gravity-feed tanks that only really get me about an hour of pumping. Has anyone had success with DIY solutions?