keeping bleached hair platinum

I have bleached and toned my hair to platinum twice in the past using Clairol Basic White and Roux Fanci-Full White Minx. Each time, say after one or two weeks it would turn yellow with a little bit of brass. After this the rinse stopped working and only turned my hair a dirty grayish, yellowish, orangy color.

I will be bleaching my hair again this weekend and this time I want to keep the yellow out. Can someone give me any advice and/or product recommendations?

I was thinking about Jhirmack Silver Brightening Hair Shampoo or Clairol Shimmer Lights. Has anyone had any luck with these?

Thanks.    

I heard the Schwarzkopf Iceflower mousse is a non-damaging toner to use that is more potent and longer lasting than purple shampoos. It should last about a week if you wash your hair everyday.

I have never had any luck with ANY toners, rinses (like Roux Fanci-Full) or shampoos like Shimmer lights - they all turned my hair a nasty grayish shade and didn't get rid of yellow, either.  I switched to Manic Panic Flashlightning bleach, and I was amazed to see a lovely platinum blonde -without using  any type of toning product -  and it stays that way! I didn't do my roots for almost 4 months, and the lightened part of my hair remained the same nice white blonde.  The only down side is that although Flashlightning worked really well for me, it dries the hair quite a bit and some front pieces even broke off.  However, with protein treatments, it recovers.