If you can smell the sewage

The EPA advises:

* Your wastewater treatment system may not be working if you can smell sewage from the general area of the tank and percolation area; have slow-draining toilets, sinks or drains or backing up of sewage at the inlet, overflow of wastewater from the tank, or ponding of sewage on the percolation area, or discolouration of nearby watercourses with greyish slime growths.

* Roof and yard water should be excluded from the system.