First, there is a difference between vacating a record and sealing a record. For the purposes of my response, I will assume that you mean vacate.
I am not familiar with Precheck. I'm assuming that it is an independent background check company. If you had a Neg 1 vacated then the conviction should not even show up. Washington law states that if the court vacates a record of conviction then you may state that you have never been convicted of the crime. However, an FBI background check should always show your arrests and all crimes that have been charged.