Some people warn very clearly about using the WW as the meth container...
http://www.e90post.com/forums/showthread.php?t=687279
If you do this setup, perhaps it's best to only use water and add a bit of meth to stop rust from forming in the insides. 50/50 mix may already be too high.
Water is what i wanted to use for anti knocking; the meth is just a nice little extra, but obviously WW is not meant for meth, so make sure you do not run a high meth percentage with this setup.