Went to get some grass (4)
I believe the answer is:
weed
This clue is a double definition.
'went' is the first definition.
('go' can mean to urinate)
'some grass' is the second definition.
(thesaurus)
'to get' is the link.
(Other definitions for weed that I've seen before include "Marijuana (slang)" , "Went" , "Useless plant - useless person" , "Unwanted plant - cannabis" , "Made water" .)