A grease-stained piece of cardboard lies in the doorway.
"How many wives would allow that?" Pete Simpson asks - his Scottish accent as broad as his smile - before explaining the importance of this oil container place mat.
Being situated indoors means the contents are already at room temperature of about 15degC and only need a boost of 65degC before reaching the optimum temperature to power Mr Simpson's 1987 Toyota for free.
Don't get swept away by the facts that he spends about two-thirds less on fuel and has run his four-wheel-drive on chip fat oil for 25,000km over the past three years - getting the good oil is a grubby process.
"Fat is ugly, messy, dirty stuff."
The research and development road to success was paved with pitfalls as Mr Simpson (36) laboured "to find the best way of taking a tub of chip fat and turning it into fuel".
The idea began six years ago when Mr Simpson and his wife Carol arrived from Britain and a Hawea Flat local asked him if he was interested in making biodiesel.
"Our house was falling to bits. We had one brand new child, new job, new life, so I said 'no way'."
Fast forward two years and, armed with a book on biodiesel and a "minefield of information" off the internet, Mr Simpson began his mission.
He soon realised that his experimental inklings lay not in manufacturing biodiesel but in modifying his vehicle to run on 100% fat.
A part-time job at Wanaka Wastebusters had introduced him to the world of recycling, so he salvaged materials to make the conversion.
The inevitable mistakes and breakdowns occurred, prompting Mr Simpson to investigate how temperature "massively" affects the behaviour of oil.
To achieve combustion, the chip fat oil must be heated to the same viscosity as diesel for it to be injected into the engine.
If it doesn't reach the necessary temperature of 80degC then it will clog the fuel filter and cause the lift pump to struggle, because it is trying to suck up much thicker fuel.
To heat the chip fat oil, he uses a two-tank system.
The Landcruiser is started using diesel from an 8-litre auxiliary tank and once his home-built heaters and the engine's warmth boost the alternative fuel source up to 80degC, he can "flick the magic switch".
A typical 18km trip into Wanaka necessitates running the car on diesel for about 4km before stopping to flick the under-the-bonnet brass tap to the chip fat oil tank, and then back again to diesel, about 4km from his destination for the cool-down period.
"About 99.9% of people would not be bothered to do that."
To combat the Central Otago winters, the car's filter and fuel lines are insulated and the filter is set on an automatic thermostat.
A "self-taught" mechanic, Mr Simpson estimates he spent about $1000 on parts and wiring to make the changes to his car.
Then there was the "thousands of hours" spent on learning about the oil and, secondly, getting to grips with the Landcruiser's internal workings.
After about 2000 litres of chip fat oil, the costs were recouped.
They would have been far higher had he not performed the work himself, Mr Simpson said.
He then discovered that if the oil was left for longer (up to 18 months), the filtration process provided him with purer oil, which in turn equals better fuel economy.
The 4.2 litre non-turbo Toyota averages about 8 litres per 100km.
This figure is 10% less than it should be but the downside is that it is coupled with the same percentage less of power.
Mr Simpson collects the chip fat oil from local restaurants in 20-litre containers, then stores it in 1000-litre tanks for 18 months.
Once the fatty residues have settled to the bottom, he pours the oil, through a filter, back into a smaller container, from which he fills up the vehicle.
After enduring jibes from autoelectricians, engineers and protesting howls from his family during the fairly regular roadside repairs, Mr Simpson still feels like he has had the last laugh.
"Now I'm quite chuffed that my car hasn't broken down . . . yet."
