Sign on vacant premises including one dunny (6)
I believe the answer is:
toilet
This might be a double definition.
'sign on vacant premises' is the first definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps you can see a link between them that I can't see?
'one dunny' is the second definition.
The definition suggests a singular noun which matches the answer.
'including' is the link.
Can you help me to learn more?
(Other definitions for toilet that I've seen before include "Lavatory paper" , "something to go on?" , "WC" , "where penny the cost?" , "Plumbing fixture" .)