“I have a carpenter friend with a DuraMax diesel who has been collecting grease and making his own fuel for years.”
And your friend is not paying the associated road taxes that are levied on fuels.
If I were him I’d not tell anyone I was doing this or the state will will charge him with a crime. I knew a farmer back in the late 1970’s that converted his truck to LP Gas using a kit for a tractor because it was cheaper than gas and he got into a lot of trouble.
Big Brother wants his tax money from motor fuels.
Please note. I have no animosity towards your friend - but he needs to be very careful unless he is paying the fuel taxes on the bio-diesel he makes
If not, he certainly won't get any grief from me. Where we live highway taxes are pissed away on social projects.
The dead give away for the DOT guys is the exhaust of these users smell like French fries or whatever the oil has been used to cook.
Also this fuel gets real thick when it gets cold, say below 32 degrees and requires heaters to keep it from solidifying.
A friend of mine made and sold these filtration systems. Started a few years ago when fuel costs were very high. He ended up selling more overseas than here in the US because it is a tedious and messy way to go. It takes time to go round up used grease every day or so and fast food places now have caught on to the scam.
Me, I would rather spend my time being more productive generating more income in order to buy fuel than waste time with this time consuming messy, messy system.
By the way, the last I heard the states were working on laws requiring all manufacturers of these systems to report citizens that buy the things. If you did not report your mileage and pay your road taxes you got a visit from the tax man.