| Paul, this is the relevant point from the rules.........
"1.6.11 Fuel Tank
Fuel tanks must be either OEM Ducati OR made of steel or aluminium.
Fuel tanks with tank breather pipes must be fitted with non-return valves that discharge into a catch tank with a minimum volume of 250cc made of a suitable material."
The later 620ie's are supplied as standard with the "plastic" tanks, so the "OEM" statement validates these as OK to use. | 
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