Went backwards, a long way down (4)
I believe the answer is:
deep
'way down' is the definition.
(I've seen this in another clue)
'went backwards' is the wordplay.
'went' becomes 'peed' (both can mean urinated).
'backwards' says the letters should be written backwards.
'peed' backwards is 'DEEP'.
'a long' is the link.
This may not be right. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for deep that I've seen before include "Profound - cunning - sea - bass" , "Intense; low (in pitch)" , "Profound - engrossed" , "Heartfelt" , "Intense -- extreme" .)