Having a tenant, he goes where memories can be washed away (5)
I believe the answer is:
lethe
'having a tenant he goes where memories can be washed away' is the definition.
The definition suggests a singular noun which matches the answer.
'having a tenant he' is the wordplay.
'having a tenant' becomes 'let' (I can't justify this - if you can you should believe this answer much more).
'let'+'he'='LETHE'
Can you help me to learn more?
(Other definitions for lethe that I've seen before include "In Greek myth, the river of forgetfulness flowing through Hades" , "Mythological river in Hades" , "Ethel's mythical river of forgetfulness" , "River whose waters caused the souls of the dead to forget completely their life on Earth" , "where elephants never drink?" .)