Because Aerobic Treatment Units (ATU) force air into the system to encourage the aerobic bacteria growth the process can leave a very distinct odor. Some people compare it to an old basement smell, others say it is a musty odor but not really unpleasant and some say they smell the hydrogen sulfide being produced leaving the rotten egg odor. We at TankTechsRX do not believe any odor should be present. We are not sure what “musty but not unpleasant” means and we have been in old basements and no two smelled alike. We definitely avoid rotten egg smell. For us, odor should not be present at a noticeable level. The typical solution is to move the vent stack pipe to a level or place where the odors are less noticeable. TankTechsRx used in an ATU will remove the odor to a level below what the average person will notice or recognize as a septic. Remember it does take a little time for our bacteria to multiply to the point it captures the entire tank, but once it is captured, TankTechsRx for Septic Systems will keep it under control.