Dragon's blood for those tedious household tasks

[Amy Z]

No: HPFGUIDX 15979

There was some back and forth a few days ago regarding whether the 
12th use of dragon's blood, or indeed any use, is ever mentioned in 
canon.  I didn't think so, but knew I'd read about it somewhere.  I 
finally tracked it down.  It was on Jenna's page, which I cannot for 
the life of me find (unless this is it), but here's the same 
information.  It was given as a rumor on the "facts and rumors" page 
below.  "Tom Riddle reports: 'The twelfth use of Dragon's blood is 
oven cleaner!'" 

http://potterinfo.tripod.com/rumors.html

Tom Riddle, eh?  Not the most honest guy.  However, the following 
article quotes a more reliable source: "J.K. Rowling says the twelfth 
use is oven cleaner."  

http://www.kids.infoplease.lycos.com/spot/harrypotter1.html

Amy Z
who never cleans her oven--
just running it at 500 degrees for awhile does the trick, right?