No, you don't need a license for a "pusher" in your house, just if you operate them on location.
As to slot machine possession, Washington is a "25 year" state. If the slot machine is older than 25 years you can legally possess it as an antique. It may not be used for commercial gambling (put on location). Pachislo (skill stop) Japanese slots are 100% illegal in this state and will be siezed and destroyed.