Get Rid of Sweat Stains

Problem: I use shirts every day at work, and I really dislike using any kind of t-shirts underneath. There's a flipside to this. After using the shirt for some days, I get the not so good looking yellow sweat stains on my shirts. Getting rid of them also used to be a problem with regular detergents and wash. I've found a solutions though..

What you need:
1.) Vanish Oxi Action (Europe) or Oxi Clean (US version). You should get the regular powder version for coloured clothes.
2.) A toothbrush
3.) A cup
4.) A towel is prefered

Put a scoop of Vanish Oxi Action/Clean in a cup, add some (not much) lukewarm water, and mix it all good together for a while with the toothbrush. Gather all your shirts, put them in a pile ready for wash in front of you. Sit down on a chair and put the folded towel on your  lap (so you don't "wet your pants"). Next take a shirt a time, and use the brush to apply a decent amount of your mix on the spots you want to get rid of. I usually brush and apply for about 15 seconds each. Next just put each shirt in you washing machine, and about 5 minutes after the last shirt give it a regular wash. I usually put the leftovers from my Vanish mix into the washing machine as well.