I want to thank all of you for this valuable info. Our 2014 tt has been on 3 trips and the ammonia smell inside was toxic - it made my eyes water. We tried all tricks we could find on line, the Calgon softener, ice cubes, bleach, vinegar, checked the vent and nothing worked. Last Sunday as a last resort I hit the web and found this site. We ripped out the toilet and it was FOUL!!! Called Diane at Dometic (told her she was reaching rock star status on this site) and a new toilet will be here Thurs. However - it's a new, improved 300, which had us concerned. We decided to order a 310 from CW and are going to sell the 300. Thanks, again!!!!