I wouldn't recommend this method t anyone. His water washing is wrong although he did mention the air bubbler. The separation of the (soap) is important before you wash because it is preferable to heat the bio to separate the methanol. (the methanol can be reclaimed) Filtering is absolutely critical in maintaining engine reliability. If you use bottles of cooking it cant possible be economical. Methanol in oz is around $400 / 205litre drum now. Finished product needs to be filtered down to 1-5 microns for the various types of modern engines. In practice the fish and chip shop oil usually poor quality to start with and often burnt due to over use and it takes a lot of time to set up a good pre-filtering gravity system to minimise work and costs involved. (as opposed to a pumped system using replaceable filters) If you dont know what you are doing using poor quality bio in a common rail engine is fraught with danger of engine damage. You will find all things considered, around a $/litre is where you will be at.
