How to un-stain stained test tubes

[SCU33ZE]

we all are confused when we do a ph test in a yellowish glass tube,,it changes the color a bit and we make mistakes,,so heres a recipe to unstain them(for Aqua. Pharm. )fill with alchohol(90%) to white line,,,then add 10 drops of that ph down u never used,,shake ,,leave for 10 minutes and drain,,i boiled mine just to get rid of the achohol smell and stuff,,,thats it,,if u already done this ,,good for u....,

if you tried this, post with your results