Well-filled vessel (6)

I think it could be either:

Which length description are you looking for?:

3-6

tanker

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'vessel' is the definition.
(tanker is a kind of vessel)

I don't understand how the remainder of the clue works.

(Other definitions for tanker that I've seen before include "Fuel carrier" , "Big ship for transporting oil" , "'Ship, carrying crude oil say (6)'" , "Bulk oil carrier" , "Bulk-liquid lorry" .)

I've seen this clue in The Globe and Mail.

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