RPC 5.1 says:
(a) A partner in a law firm, and a lawyer who individually or together with other lawyers possesses comparable managerial authority in a law firm, shall make reasonable efforts to ensure that the firm has in effect measures giving reasonable assurance that all lawyers in the firm conform to the Rules of Professional Conduct.
(b) A lawyer having direct supervisory authority over another lawyer shall make reasonable efforts to ensure that the other lawyer conforms to the Rules of Professional Conduct.
(c) A lawyer shall be responsible for another lawyer’s violation of the Rules of Professional Conduct if:
(1) the lawyer orders or, with knowledge of the specific conduct, ratifies the conduct involved; or
(2) the lawyer is a partner or has comparable managerial authority in the law firm in which the other lawyer practices, or has direct supervisory authority over the other lawyer, and knows of the conduct at a time when its consequences can be avoided or mitigated but fails to take reasonable remedial action.
There are no Washington Supreme Court cases dealing with RPC 5.1. There are, however, three WSBA Advisory Opinions.
A useful discussion of RPC 5.1 can be found in Advisory Opinion 2219 (2013), RPC(s): RPC 1.0, 5.1(a)-(c), 5.5(d)(1), Subject: General Counsel Responsibility for In-house Lawyer