Official Explanation
"The song "Message To Harry Manback" on Tool's Ænima album is an actual message left on Gary Helsinger's (Hotsy Menshot) answering machine by a former friend from Italy, who Gary had just kicked out of his apartment for stealing his roommate's belongings. "Harry Manback" is a reference to routine from the late comedian Bill Hicks. Maynard James Keenan and Danny Carey were both roommates of Bill Manspeaker during Green Jello, and Gary was later roommates with Maynard as well as Billy Howerdel of A Perfect Circle. "
http://en.wikipedia.org/wiki/Green_Jelly
So could it possibly be a Green Jello/Bill hicks tribute all rolled into one?
I thought that this was common knowledge.