They act in collusion with each other to cover up the truth.

他们沆瀣一气，试图掩盖真相。

They act in collusion with each other for profit and did many bad things.

他们为了利益沆瀣一气，做了很多坏事。

Those corrupt officials act in collusion with each other to oppress the people.

那些腐败官员沆瀣一气，欺压百姓。

These two companies act in collusion with each other to manipulate market prices.

这两家公司沆瀣一气，操纵市场价格。