For the Levamisole:
The dosage is 40 ppm - 6 hours to kill the Montipora eating nudibranchs I believe, but it's a good idea to blast the coral with some water afterward as sometimes I think they are just stunned and not completely dead. I believe the Acropora eating flatworms don't need as much time, but I've never had the chance (thank the stars) to experiment with them.
If you are using the powdered form then it's 90% active, therefore you need about 44 ppm, or approximately 44 mg/liter. Pretty hard to measure the really small quantities. I found that the really tiny spoon that comes with Chemi-clean will measure out exactly 0.103 g of the powdered Levamisole, therefore good for 2.3 liters worth.
If you are using the 13.65% active liquid solution then I believe 40 ppm works out to 1.1 ml/gallon of dip water. Mitch Carl seemed to prefer the powdered form.
Interceptor: The big dog tablets (51-100lb dogs) will treat 380 gallons. If you grind up the tablets use 25 mg/10 gallons dip or tank water. Treatment is 6 hours duration to kill the Acropora red bugs, or the Montipora black bugs. Some people use 10X this dose with no problems. Some people also shorten the duration of the dip.