(1) A determination as to whether a subject has a foreign substance in his or her mouth will be made by either an examination of the mouth or a denial by the person that he or she has any foreign substances in their mouth. A test mouthpiece is not considered a foreign substance for purposes of RCW 46.61.506.

(2) If during a breath test, interference is detected, this will invalidate the test. The subject will be required to repeat the test. A subject whose breath registers the presence of interference on two or more successive breaths shall be deemed to have a physical limitation rendering them incapable of providing a valid breath sample.

(3) In the event that the instrument records an "invalid sample" result at any point during the subject's test, that subject's test should be readministered, after again determining that the subject has no foreign substance in their mouth as outlined in WAC 448-16-040(1), and repeating the fifteen minute observation period.