Free shuttle ride from SeaTac baggage claim outside carousel #15 at the end. There will be a sign and queuing ropes. Avis is on the 2nd floor so catch the elevator or make sure you are on the escalator that goes to the 2nd floor. Not all escalators do. Easy free shuttle ride back to SeaTac.
There is a shuttle from SeaTac. It's free, looks like a regular bus but has a bunch of car rental logos on the top. It also picks you up at a different spot than the hotel shuttles. Just look for signs near baggage claim.
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