How do I get rid of a musty smell in my kitchen sink drains?

My husband used some power plunger thing and blew out the pipes in our kitchen, now there is a musty smell sometimes from the drains. Is there something still in the drains? Any ideas on how to get rid of the smell?
Update: Thank you all! What a helpful section. I think I'll hang out here instead of Religion and Spirituality. They get really intense!
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