This is an interesting topic for us, as our 6-month old TT sometimes has a urine smell in the head, but not all the time. We only use it for peeing (seriously) and never put toilet paper in it! I've tried every known odor control, use plenty of water to flush, clean up any possible splashes and rinse the black tank religiously after dumping. Our dealer checked out the installation of the head and the black tank assembly, but found no problem. Now I'm wondering if the toilet is cracked inside or the lower seal is bad. But since we've never pooped in it, taking it apart mightn't be too bad. I hope. :R