Phosphoric acid also goes by E338, orthophosphoric acid, and phosphoric(V) acid. The required final concentration is 3%; the same as lemon juice.

The classic coke flush uses 5 fluid ounces and Dr Sutter uses 4 ounces. If you buy 75% solution and required potion strength and quantity is 5 fluid ounces (142 ml) at 3%.

You require 4.8 fluid ounces of water and 0.2 (5.6 ml) fluid ounces of 75% solution. As you can see the quantities of concentrated acid are small so you have to be very careful.

The mixing ratio is given by the solution bought divided by the required solution minus one

Eg (80%) (80/3)-1 = 25 {25 parts water to 1 part acid)

(25%) (25/3)-1 = 8 {08 parts water to 1 part acid}