Septic Tanks

Our range of septic tanks are suitable for both domestic and commercial applications. Both the vertical and horizontal style septic tanks can be supplied and from a starting price of £399.00. The size ranges from a 2000 litre through to 50 000 litres for specialist uses such as caravan sites, pubs or hotels.

Drainage systems

A full range of pipe work systems to compliment the tank systems. The two main systems we sell are the CorriPipe twin wall system and the Hunter Dyka sewer drain Please find information on the down load page and illustrations on the gallery page.

rain harvesting

Knollands supply small domestic rain harvesters and large commercial systems for high usage organisations such as farm dairies to car washes. Convenient packages that include everything you need to start rain harvesting through to larger more diverse projects that will benefit your pocket and the environment.

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What is a septic tank?

A septic tank consists of a tank made from usually GRP and sometimes Polyethylene ranging in size between 2000 – 50 000 litres in capacity. They are connected to a foul water pipe at the inlet and a drainage outlet pipe at the other for discharge into a soak away or further Bio-Treatment systems at the other. The design of septic tanks are vertical or horizontal and incorporate two or possibly three chambers which are separated by a dividing wall or walls that have openings / pipes to allow flow through the system.

How do septic tanks work?

Wastewater enters the first chamber of the septic tank, allowing solids to settle and scum to float. The settled solids are anaerobically digested reducing the volume of solids within the septic tank. The liquid component flows through the dividing wall into the second chamber where further settlement takes place with the liquid then draining into a soakaway or maybe lifted to another system for further treatment system.

Waste that is not decomposed by the anaerobic digestion eventually has to be removed from the septic tank, or else the septic tank fills up and undecomposed wastewater discharges directly to the drainage field. Not only is this bad for the environment, but if the sludge overflows the septic tank into the leach field, it may clog the leach field piping or decrease the soil porosity itself, requiring expensive repairs.

Where can I buy septic tanks?

If you're looking to buy a septic tank online then go to You can also buy a septic tank direct from Knollands. We can offer advice and guidance to help you buy the right size and specification of septic tank for your project which is suited to your individual needs. Our septic tanks downloads page holds a wealth of information relevant to planning your septic tank purchase if you would prefer to do some research yourself, however we are only a phone call or email away if you need help.

How often do you have to empty septic tanks and how long do they last?

How often septic tanks have to be emptied depends on the volume of the tank relative to the input of solids, the amount of indigestible solids and the ambient temperature (as anaerobic digestion occurs more efficiently at higher temperatures). The required frequency varies greatly depending on jurisdiction, usage, and system characteristics. Some health authorities require septic tanks to be emptied at prescribed intervals, while others leave it up to the determination of the person on charge of the septic tanks maintain ace. Some septic tank systems require pumping every 3 – 6 months if used as a primary tank and some may go several years without being emptied. Contrary to what many believe, there is no exact timing on how often septic tanks should be emptied. An older septic tank system which is undersized say by a large family will require much more frequent emptying than a new system used by one or two people.

Emptying of a septic tank to often or complete emptying can do damage to the aerobic bacterial colony which lives within the tank. This colony of bacteria is what breaks down and absorbs the organic matter into the tank. This is why it is important not to empty a tank fully. The anaerobic decomposition is rapidly re-started when the septic tank re-fills. A properly designed and normally operating septic tank system is fairly odour free and, besides periodic inspection and pumping of the septic tank, can last for years.