soil (one's) hands
To partake in especially underhanded, illicit, or illegal work or activities. The public can't be allowed to think that I, a senate hopeful, would ever soil my hands with a tax-evasion scheme such as that.
get one's hands dirty and dirty one's hands; soil one's hands
1. Fig. to get closely involved in a difficult task. You have to get your hands dirty if you expect to get the gutters cleaned out.
2. Fig. to become involved with something illegal; to do a shameful thing; to do something that is beneath one. The mayor would never get his hands dirty by giving away political favors. I will not dirty my hands by breaking the law.