Septic tanks use an enzyme to break down the waste so that it can pass through the filtration trench—chemicals and medicines can kill this enzyme causing the tank to smell and not break down the waste. Other things such as baby diapers and sanitary pads can cause blockages if frequently disposed into the system. Tree roots are another concern when they are planted too close to the trenches. The roots break through the trenches in search of water and will grow inside the pipe causing it to block over time requiring major repair.