I use a Potassium Permanganate solution. I leave them soaking in it until I need one, which is first rinsed well under the tap, then soaked for a few minutes in water with Prime. When the PP solution turns brown I change it.
Only downside is that it does turn my white nets brown in color :roll:
I had to order mine on the internet. It was quite a long time ago (a little goes a long way), but I think it was off of E-Bay. If you google potassium permanganate you should be able to locate someplace that sells it.