These guys regularly service the islands and I have used them many times. In fact I'm not sure if anyone else actually does service the septic tanks and greasetraps on the islands? Great service though and reasonable price. The are regulars on the island so it is easy to book a time when they are there.
The care and maintenance of a septic tank is something outside of the consideration of most urban dwellers. I'd never encountered a septic tank until I moved to a rural property in Central West NSW. Prior to that my only experience of properties without sewerage was a friend who had lived in the far western suburbs of Sydney. He was the butt of all manner of jokes because his home was still serviced by a night soil man!
Residing now on one of the Southern Moreton Bay Islands, septic tanks are again something I must contend with. Thankfully Lee's Liquid Waste Services come to the rescue and service of Bay Islanders with their fleet of 17 trucks. A family operated business for 30 years, Lee's provide a fast, friendly and efficient service. Together with septic tank cleaning they also clean drains and grease traps, deliver bulk water, and undertake non destructive digging. I recommend their services highly.