All individuals licensed in accordance with chapter 18.210 RCW shall procure a seal/stamp that conforms to the design as authorized by the board. It is the responsibility of each licensee to maintain control over the use of their stamp/seal. The impression or image of the seal/stamp shall conform to the below-illustrated design and be of a size that assures full legibility of the following required information:

(1) State of Washington;

(2) Licensed on-site wastewater treatment system designer;

(3) License number;

(4) Licensee's name as shown on license.