Vessel I can put on sea, heading west (8)
I believe the answer is:
demijohn
'vessel' is the definition.
(I know that demijohn is a type of bottle)
'i can put on sea heading west' is the wordplay.
'can' becomes 'john' (slang for toilet).
'put on' is a charade indicator (letters next to each other) (some letters go on or after others).
'sea' becomes 'med' (short for Mediterranean).
'heading west' says the letters should be written in reverse.
'med' backwards is 'dem'.
'i'+'john'='ijohn'
'ijohn' put after 'dem' is 'DEMIJOHN'.
(Other definitions for demijohn that I've seen before include "Large bottle for wine storage" , "Large bulbous bottle (with wicker cover?)" , "Large bottle enclosed in wickerwork" , "Large bottle for half-Jack?" , "Large bottle in a wicker basket" .)