The DML has (had?) a page with that info. Basically, there are a couple major variants...
Metal : has the removable lid and "Carrier" : has 4 or 5 metal tubes on the bottom : is injected family, 620, 800, 1000, 900, S4, S4R.
Metal : non-removable lid "carrier" and 2 metal tubes + level + threaded bung for the fuel outlet : carbureted monster 400, 600, 750, 900.
Plastic tanks started around 2004 and are definitely on the S2R800 and 1000. I do know that the S4Rs and S4R with Testa engines have different tank than S2R.
The fiches at ducati.com are an amazing resource:
Ducati.com
