Thank you for asking for WA advice, because it is different here than in other states if you own. If you are a renter living in foreclosed property, the incoming owner has to provide you with at least 90 day's notice. You can look this up yourself by googling P.L. 111-22, the May 2009 federal "protecting tenants at foreclosure act". Nothing in state law superscedes this. You can also get assistance from Housing Justice, a project of the King Co. Bar Association.
If you own the property, please contact http://www.wsba.org and look on their homepage for the link to the project that matches up attorneys with owners facing foreclosure. This is a project that does not cost the homeowner any attorney fees. You don't have to income qualify either. The short answer is that the Notice of Trustee's Sale, para. 10 (or sometimes "X") says that 20 days after the sale the new owner has standing to move the court to evict the ex-owner, but that just means they can file and serve a summons and complaint 20 days after the sale, NOT that the sheriff is going to show up 20 days after the sale.
In either event, there is no basis to the rumor that right after the sale anyone can toss you out. The ONLY entity with standing to effect an eviction is the sheriff. Self help evictions in WA are strictly prohibited. The sheriff will not do anything without a court order so authorizing. In order to get a judge to sign an order, a plaintiff has to wait, then file and serve an eviction summons and complaint, and if you answer timely there has to be a hearing. After the hearing, there are at least three days where the writ has to wait (long story, not relevant) and after those three days have passed THEN the sheriff has standing to show up.
Please be careful to never, ever take legal advice from a bank or a realtor. With all due respect, they are not licensed to give you legal advice. Hope this helps you. Elizabeth Powell