I need help; I have had this smell under my sink and sometimes in my master bathroom from the toilet area off and on for sometime now. The smell will be there sometimes and sometimes not (when it is there, it's obvious). The majority of the time, it will come from under the kitchen sink from the "air gap" or what I was told to put in that could suffice. I have tried to pour hot water, I've tried chemicals, and lemons and oranges, nothing seems to help. I have potpourri under the sink and while this method does help to mask the smell, it by no means fixes it! Here's the skinny: The house was built in 2008, I bought it in July of this year and almost immediately went to Home Depot and bought what the sales associate recommended to go in place of the air gap that should go on top of the sink (as my sink has no hole for it). I don't know if the smell was there before I put in the "air gap" or not; the absence of an air gap was mentioned in the inspection so I wanted to remedy the "easy" stuff. Anyway, I have noticed a putrid smell coming from under the sink; it will sometimes smell for 2 or three days in a row, then nothing (noticeable) for several days, then "IT" will come back. I will post images of what I installed and of the p-trap and dishwasher hookups if forum allows. Note: The smell was also noticed in the master bathroom about 1 month ago but that incident was isolated to that single time (not sure why or what was different). Any feedback would be welcomed; I am at my wits-end! Even if your feedback recommends I call a licensed professional, that would be welcomed too. Just noticed while trying to upload these pictures, is there a certain height above the drain the "air gap" must sit? Pics: http://www.plumbingforums.com/forum/members/fiveshinds/albums/under-sink/219-cimg6604.jpg http://www.plumbingforums.com/forum/members/fiveshinds/albums/under-sink/218-cimg6606.jpg Thank you in advance!