A Washington purchase agreement documents the sale of a piece of real property for a specified financial figure. A Washington residential purchase agreement is used when making an offer to purchase real estate.The agreement initiates the negotiation process. Description of The Property. The completed document will describe the property being sold, purchase price, closing date, and closing costs. Ensure you know the legal requirements and disclosures of a Washington real estate purchase agreement. Fill in our template to create your agreement. Download our free PDF and Word sample templates or generate an official Washington real estate sale contract.