When you clean the filter cap off you will see where it goes. At the very tip is the rubber o ring.
Use a socket to take off the housing, just go buy it, you'll need it to get the torque settings right anyhow.
If you don't do your oil change with warm oil, it'll just take longer to get out, (~45 mins) and you may not get it all out. I did mine cold, drained forever, filled up 8.5 bottles and I'm dead center on the oil levels.
How much was your oil change kit?
2003 Ducati '996
2008 M3: Sparking Graphite, Red Fox Standard, 19s, Premium pkg, Tech pkg, Premium Enhanced Sound, HD Radio, Heated Front Seats.