I have a carpenter friend with a DuraMax diesel who has been collecting grease and making his own fuel for years. He does it in a two gar garage with room to park the big truck, mower, rototiller and more. He estimates his fuel costs are a bit over a buck a gallon and the set up cost him under $300 about six years ago.
“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