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muck in
to join in attaining a common aim
muck about
To do random unplanned work or spend time idly
To do something with a piece of equipment when you do not understand how it works.
To be playful; full of fun and high spirits
muck around
To muck about.
muck out
To clean the excrement and other rubbish from the area where an animal is kept, such as a horse stable or a dog kennel.