Tradesman with his own loo on the Underground (5)

Here is my best explanation:

This could be a double definition.

'tradesman' is the first definition.
The answer and definition can be both people as well as being singular nouns.
Maybe they are linked in a way I don't understand?

'his own loo on the underground' is the second definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.

'with' is the link.

Can you help me to learn more?