Tenants in Washington must obtain explicit written consent from their landlord before subleasing a rental property. A sublease agreement is a legal contract signed between a tenant and a third party allowing the latter to rent out the entire property or any part of it.Subletting, also known as subleasing, involves renting out a property or a portion of it that you are currently leasing, to a new tenant. When a tenant asks its landlord to consent to a sublease the Landlord will rightly focus first on business concerns. Who is the subtenant? How Much Does a Sublease Cost? The average cost (i.e. Sublet and sublease are two different words for the same concept. The suffixes of each word, "let" and "lease," both mean to rent out a property. Create your Washington sublease agreement and sublet your rental.