Wiktionary
vb. (cx informal English) to join in attaining a common aim
Usage examples of "muck in".
He was standing in the center of a large low tent of air, which was floored by the velvety sea-muck in which he had sunk to his ankles and roofed by the leadenly gleaming undersurface of the water -- not evenly though, but in swells and hollows with ominous downward bulges here and there.
Like mayors before him, Rudgutter liked to compare the civilization and splendour of the City-State Republic of New Crobuzon with the barbarian muck in which inhabitants of other lands were forced to crawl.
The surface of the mound of frozen muck in the barn showed the scars of the battle.
The wait seemed interminable until the irrepressible SEAL suddenly appeared out of the muck in their midst.
Gary was gasping for breath, muck in his eyes and mouth, unable to see anything.
When he stepped into the muck in order to find out whether or not he could travel under these conditions, he was able to see the level of the viscid slop declining.
D'yu mean to sett there where y'are now, coddlin your supernumerary leg, wi'that bizar tongue in yur tolkshap, and your hindies and shindies, like a muck in a market, Sorley boy, repeating yurself, and tell me that?