Q: After being pulled over for not using his turn signal, my roommate was was coaxed into performing a breathalyzer test where he blew a .09. Before performing the test, however, he was not asked to clear his mouth of any foreign objects (of which he admittedly had none). I have read that this can potentially invalidate the test.

A: Challenge a DUI.  Section 448-16-040 of the Washington Administrative Code (WAC) requires that

“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.”

So the determination that can be made either by the officer checking the subjects mouth or simply asking them if they have anything in their mouth. So, yes, it can be an issue, built it will take the knowledge and experience of a good attorney to ferret it out and turn it into an issue that can get your friend a better outcome.