Is it leagle to evict persons on a lease for any reason the owner thinks of in Wa State?

IF there is a written lease, then they can evict only for a breach of some of the terms in the lease, if they are trying to evict for other reasons, refuse to move, let them take you to court and prove in court they do not have a valid reasons.

If this is a verbal month to month reason, they can with proper notice basically ask you to leave and then evict if you don't

A landlord cannot evict a tenant. An eviction order has to be issued by a court of law. The eviction process starts with a notice to vacate. If the tenant doesn't vacate then the landord goes to court for an eviction order. So if an eviction order is obtained it is legal. If there is no valid reason to terminate a lease, then the court woin't issue an order.