I just had my septic tank pumped two weeks ago and I can honestly say that is by far the worst smell I've ever experienced. I was driving home and the honey wagon was out back pumping my tank when I pulled into my driveway and I wasn't even half way up my driveway when it hit me. My driveway is 200 ft long btw and you could see a big cloud of methane gas hovering over the tank where the lid was removed. It was so disgusting.