I think the clear K1 has at least some fuel taxes applied to it. Does it have the "non taxable use, penalty for taxable use" disclaimer at the K1 pump? The dyed, untaxed ones do, just like an offroad street illegal pump. As far as I know they can't tell if it was taxed or not unless that dye is in there, but the reason many people get into trouble is that it is designed to be detectable for many many tanks of legal fuel after the offense occured. As to the warrant thing, I have heard various stories 1) If you have DOT #s you are absolutely required to submit 2) If you have locking fuel caps that is probable cause and you must submit to the test. 3) If you are there, that implies you can ask for a search warrant. If any of this is incorrect, someone with definitive knowledge should correct me. I'd actually like to see how a court would feel about the DOT giving someone who was actually innocent of fuel tax evasion but asked for a warrant out of principle the bad treatment Dieselcrawler described.