Hi Dodge ,
NaoH is sodium hydroxide or "just caustic flakes" and also comes in a granular form looking like salt.. KoH or Potassium Hydroxide also comes in flakes.
If you use any old Caustic soda it could have all sorts of additives or impurities added.
Dont follow the america way and use "caustic soda", just because you can get it as draino at a super market.
We at the melbourne biodiesel club who are tried and tested at making biodiesel would recommend only use pure KoH. I do not have the contact of which chemical supplier we use at hand at the moment but can find out.
If you want a quality guaranteed chemical reaction to make biodiesel you must titrate the FFA's in your oil and use KoH only in the formulae
{(T + 3.5) x 3 } x V = K
T= titration value with NaoH standard solution.
V= Volume of oil to be reacted in litres.
K= weight in grams of KoH.
good luck.

When using NaoH the formulae is (T+3.5) x V = Na
where Na is the weight in grams of NaoH.

Just dont use NaoH.

Join the Melbourne Biodiesel club.
In the future we would also like to test a "standard solution" of KoH for titration. Although we have learned from industry standards NaoH is the "Standard solution" for titration. However KoH is the preferred alkaline for biodiesel reaction as it goes into methoxide solution easier, and always creates a better result.
And the grey water from water wash can be used as a fertilizer.
Cheers,, Darren.