I was thinking maybe something like woolite used to clean sweaters and delicate fabrics?
Do the ear pads just pop off the HD600? Don't want to damage them trying to get them off improperly.
Thanks
Be a part of the community.
It's free, join today!
Can you wash the ear pads of a Grado?
Nice bump. 
Btw, here's a couple of threads on this
http://www.head-fi.org/t/161507/do-you-wash-your-grado-pads
http://www.head-fi.org/t/182805/how-do-you-go-about-cleaning-grado-pads
Sennheiser HD600/650 pads come off really easily. You just grab one side with your figers inside the ring and your palm outside the ring and pull them out with your other hand holding the yoke/driver frame. They'll pop off.
I've actually machine washed and dried my HD650 pads 5 or 6 times in the course of 4 years. This will destroy them eventually however. Because these are my only phone and they've seen continuous daily use, I think 4 years is already a very good lifespan for the pads and I don't mind replaceing them.