Howdy,
Adapter, Container NSN 5342-00-066-1235 MFR P/N: 13211E7541
Is the 5 gallon/55 gallon bung adapter which the aux fuel line connects to.

Auxiliary Fuel Line NSN 4720-00-021-3320

Auxiliary fuel hose specs
View attachment aux fuel line specs1.pdf
bung adapter in 5 gal MFC

In a 55 gallon drum you use both pieces
Adapter, Container NSN 5342-00-066-1235 MFR P/N: 13211E7541
Is the 5 gallon/55 gallon bung adapter which the aux fuel line connects to.

Auxiliary Fuel Line NSN 4720-00-021-3320

Auxiliary fuel hose specs
View attachment aux fuel line specs1.pdf
bung adapter in 5 gal MFC

In a 55 gallon drum you use both pieces