coolant petcock location ?
 

2004 A8L

want to bleed the coolant.

where are the coolantdrains ?
they are not obvious.

thank you

I don't know every variation - but most don't.
You have to remove the under-tray and disconnect the coolant lines that run to the gearbox. Links to the service manual PDFs are here...
D3 Tech dump - A8 Parts Forum
eg file 8 - page 171