Usa models are equipped with an additional system with an evaporative emissions canister that prevents fuel fumes from being discharged into the atmosphere.
The breather hose (4) is connected to the canister filter (1); when the fuel has been filtered, it is returned through the hose (2) to the horizontal (a) and vertical (b) intake manifolds via the hoses (2a) and (2b). Drainage pipe (c) and the hose (5) vent to the ground.
For correct positioning of the connection hoses consult the indications given below.

Evaporative emissions canister
Removal of the evaporative emissions canisterCharging the battery
Before charging the battery, it is recommended to remove it
from the motorcycle.
Important
The battery is housed in the cowling, always contact
a ducati dealer or an authorised service centre for its
removal.
Remove the left cowling (1, fig. 137) Loosening:
side screw (2, fig. 137) Retaining ...
Reassembling the front footrest brackets
To reassemble the brackets (6) and (21) carry out the removal procedure in
the reverse order; tighten the screws (7) to a
torque of 25 nm +/- 10% (sect. 3 - 3, Frame torque settings).
...
Clutch cover
Clutch-side crankcase cover
Screw
Screw
Oil level sight glass
Screw
Plate
Bush
Sealing ring
Shim washer
Circlip
O-ring
Locating bush
O-ring
Plug
Sealing washer
Screw
Plug
Panel
Spare parts catalogue
Diavel abs clutch-side crankcase cover
Diavel carbon
a ...