Go to www.ritdye,com  Click the "Techniques" button, and start reading.  The reason for this is that these people have forgotten more about dyeing than I know, so read up.  You can probably skip the "Creative Techniques" and a few of the FAQs.  Rit suggests that a small amount of laundry detergent sometimes be used.  If you do so, [b] use Woolite detergent only.  The reason for this is because many other detergents can mess up clothing's IR/NVG signature by adding optical brighteners to the clothing.  Woolite doesn't have any brighteners.  They will also tell you how to estimate the amount of dye needed.