Concrete sectional septic tanks were seen as a quicker and cheaper option to the traditional brick built systems, this was of course prior to the emergence of modern fiberglass and plastic tanks.

There are plenty of them out there and given that the majority of them will be over 40 years old it is little surprise that they will require some attention.

How Concrete Sectional Septic Tanks Work

These circular tanks consist of one central holding chamber and an outer filter media chamber, the initial flush enters the central chamber where the lighter waste floats to the top of the tank forming a crust and heavier sediment settles to the base.

The displaced waste water then overflows through into the outer chamber where a small ledge disperses it into the filter media which would normally be clinker or washed stone, the water then filters through the media and finds it way through to the tank outlet.

As with any septic tank bacteria and enzyme set to work on the crust that forms in the central chamber and regular emptying is required to remove the sediment at the base of the tank and to ensure the crust does not become excessive.

Why Concrete Sectional Septic Tanks Fail

The tank walls themselves tend to be structurally sound and water-tight but the tank covers do get damaged particularly the thinner slabs covering the central chamber, more often than not it is the filter media that becomes clogged with silt, fibres and debris.

When this happens the filter media has to be excavated, washed and put back or it has to be removed from site and replaced. As the image to the right shows the outer media chamber is very narrow and usually around 1200mm to 1500mm deep so specialist post shovels have to be used.