1. 一起干活;一起出力;参加
If someone mucks in, they join in with an activity or help other people with a job and do not consider themselves to be too important to do it.

e.g. Course residents are expected to muck in and be prepared to share rooms...
场地附近的居民也将会加入并分享自己的住处。
e.g. She mucked in with the chores and did her own washing and ironing...
她也一起做些家务杂事，并自己洗熨衣服。