come clean的意思是“全盘招供；和盘托出”。

I thought it was time to come clean (with everybody) about what I'd been doing.

我认为到时候了，该（向大家）说清楚我一直在干些什么。

和clean相关的一个搭配还有make a clean breast of it，也是全盘招供的意思。

Julia finally made a clean breast of it and admitted that she had stolen the money.

朱莉娅最终坦白了，承认是她偷了钱。