Found a little more detail in the 1999 Pharmingen Catalog (p. 921)

1.	Prepare the following aqueous solutions:
		0.2M Potassium Permanganate (31.6 g/L)
		2.0M Sulfuric Acid (112 ml concentrated acid/L)
2.	If necessary, dilute DAB solution. It should not be over 0.9 mg/ml.
3.	For each 10 ml of DAB solution add:
	5 ml 0.2M Pot. Permanganate
	5 ml 2.0M Sulfuric Acid
4.   Allow mixture to stand for at least 10 hours, during which time the DAB
will become non-mutagenic.
5.	To decolorize solution, add powdered ascorbic acid.
6.	To neutralize decolorized solution, add sodium bicarbonate.  Test
for neutrality.