More reliable plumber (7)

I believe the answer is:

sounder

I'm a little stuck... Click here to teach me more about this clue!

This could be a double definition.

'more reliable' is the first definition.
(I've seen this in another clue)

'plumber' is the second definition.
Both the answer and definition are comparative adjectives. Perhaps you can see a link between them that I can't see?

Can you help me to learn more?

I've seen this clue in The Irish Independent.

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