Demonstrated how to fill tin (5)
I believe the answer is:
shown
'demonstrated' is the definition.
(thesaurus)
'how to fill tin' is the wordplay.
'to fill' indicates putting letters inside.
'tin' becomes 'sn' (Sn is the chemical symbol for tin).
'how' going within 'sn' is 'SHOWN'.
(Other definitions for shown that I've seen before include "Demonstrated" , "Displayed" , "Explained" , "Exhibited" .)