depends on how your fishing it,
If i’m fishing shallow, i’ll riddle the soil off the worm first making sure i keep the riddled soil, then wash the worm in the water in a fine mesh net to get the larger lumps of soil to break down, put the worm in a bait box chop it up (its easier to chop without the soil off) then i’ll add a couple of pints of caster and then put the riddled soil back in the tub and mix the whole lot up. this should give a nice cloud when cupping in.
For fishing on the deck with worm I do the same process but don’t use the riddled soil instead i keep it for the next time i’m fishing shallow