put the whole helmet in the washing machine - yeah, that will go well.

Be careful with cleaners because helmets can be ruined easily by pretty common chemicals. I spilled rubbing alcohol on a helmet once and it heavily discolored both the styrofoam and the shell.

Talc draws grease out sometimes. I had a chamois cream one time that contained talc and I discovered by accident it was really good at removing chain grease from clothes.