A few years ago, I managed a brand new villa. Meaning, not quite ready for rental guests. The contractor never hooked up the septic system, so the tank became a holding place for unprocessed human waste, and the scent became unbearable. And of course, the owners ran out of money, so were unable to properly fix this problem.
Got an email from xxxxx and also talked to the manufacturer of the waste system. They are more inclined to think that the problem with the smell is with the holding tank and stagnate water. If the system was not working properly, then you would hear the alarm, which is a beeping sound. First dump the holding tank water with a submersible pump and then use vanilla extract to sanitize the walls. The vanilla extract will cut any odors, all you have to do is spray or splash it around the inside. When we get the landscape done we will have an irrigation system put in that uses that holding tank water and will keep it from stagnating. In the mean time you will just have to keep an eye on it.