1 milliliter of 12% added to 10 liters of water is the same ratio as adding 1 liter of 12% to 10,000 liters. (I usually do it in gallons but the ratios are exactly the same).
So test your tap water and get a baseline FC reading.
Then put 10 liters of tap water in a bucket (since even in the US 2-liter soda bottles are everywhere, 5 of those works).
I use a drug-store eyedropper (glass, of course) with measures on it already for 0.5 and 1.0 ml. Add 1ml of 12% to the 10 liters and mix it up. Let it sit for 10 or 15 minutes.
Measure with your K-2006 FAS-DPD test to find the chlorine level, and subtract the FC of the tap water.
The resulting measure is the actual concentration of your liquid chlorine.

(This comes from the formula for ppm: Parts per Million.
((1,000,000liters/10,000liters [pool volume]) * .12 * #liters of chlorine) = ppm, where .12 is 12% strength liquid chlorine. You can substitute .0525, .06, .105, or .125, depending on the claimed concentration. # Liters is assumed to be 1, but can be more. Again, it works just as well if you substitute gallons for liters everywhere. I simply reduced it from 1,000,000 liters to 1,000,000 milliliters, pool volume to 10,000ml and # Liters, becomes #ml.)

Carl