Washington law allows you to ask the court to "vacate" certain misdemeanor and gross misdemeanor convictions. The particular law is RCW 9.96.060.
When a conviction is "vacated", it means that you're released from all penalties and disabilities resulting from the offense. The conviction can't be included in your criminal history in determining your sentence in any later case. For all purposes, including answering question on employment or housing applications, you may state that you have never been convicted of that crime.
For a brochure on vacating convictions please click here.