Reading Services - How your septic system works

A septic tank is a form of holding chamber utilising a form of internal construction to slow down the flow through the tank unit. The outlet from the septic tank leads to a soakaway system below the ground surface. The diagram shows a traditional single septic tank having just one chamber and using inlet and outlet T pipes. This is the simplest form of septic tank and works as follows:


1. Sewage enters via the inlet T pipe (A)and discharges to the lower of the tank.

2. Gravity pulls the solids in the sewage to the base and via anaerobic biological action, a scum layer can form on the surface (B).

3. Effluent (with a very low solids content) leaves via the oulet T pipe (E). This can then enter a second or third chamber and then leads to a soakaway field drainage system.

The principle of a septic tank soakaway is to disperse septic effluent (sewage without a high concentration of solids) into the sub soil at the site. The size of the soakaway will be dependant on the following factors:

1. The porosity of the sub soil material.

2. The size of the property and the number of residents it is serving.

3. The type of treatment system, i.e. a septic tank or a sewage treatment plant.

Common septic tank soakaways are constructed via long trench lines filled with a clean stone and have a slotted or holed distribution pipe. These trenches can be interconnected (a looped system), a simple long trench, a herring bone layout or a large filled pit.

Whichever system you have, the tank must be emptied on a regular basis to ensure that solids do not enter the soakaway.

Q. Why should I empty my septic tank?

The reason for emptying your septic tank is to remove the solids which may, eventually, block your soakaway. The key to a well functioning septic tank is the soakaway. If the soakaway becomes blocked, the tank will fill quickly and need emptying before it overflows.

Q. Do I need to empty the tank ?

Yes !
The soakaway is the key to the system. It is important to have the septic tank emptied at the correct intervals, otherwise there may be an excessive build up of sludge. Once sludge has entered land drains, it is difficult to regain their porosity, which could mean replacing the soakaway and the surrounding soil/gravel. Although the bacteria (anaerobic digestion) breaks down the solids, excessive use of detergents and disinfectants can kill off bacteria.

A sign it needs emptying:

Slowly draining sinks, toilets, baths etc
Tank covers lifted by overflowing solids
Backing-up of sewage at the inlet
Surface flooding 'downstream' of the tank
The system backs up to and beyond the drain inspection chambers
Polluted water in ditch or watercourse
A smell of sewage in the area
If you have just moved into a property and have no idea when it was last emptied, now would be a good time!
The time to get a tank emptied is before you have a problem.

Q. How often should a septic tank need emptying ?

There is no rule of thumb for how often tanks should be emptied.
An older system with an undersized tank that is being used by a large family will require much more frequent pumping than a new system used by only a few people. How often the septic tank has 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). We often find the level of the water table, and the season/weather have a great impact.
Remember the soakaway pipes let water from your tank soak into the ground when dry; but when very wet the process can be reversed!

Q. Why is my tank full after only a few weeks ?

The only time a septic tank is empty is just after emptying !
A septic tank works when it is full. When the tank is full, and in good working condition, the liquids will drain away via the soakaway. The average person uses (approx) 150ltrs of waste water per day. Therefore a house with 3 people in it could use 13,500 ltrs of waste water a month. A standard tank is 4500/9000 ltrs.

Q. What problems can I get with a septic tank ?

The main problem which happens is the soakaway becoming blocked. This can be due to lack of maintenance or from the soakaway being damaged by nearby tree roots and bushes. A septic tank or cesspool can overflow or leak which is an offence under the 1936 Public Health Act. A tank can crack in very cold weather enabling ground water to enter it.

Q. Septic tanks don’t need emptying.

It’s not true !
Many people (usually older people) often say “ I don’t know why I’m having a problem, it was emptied 10/15/20 years ago” Tanks in older houses were installed to cope with the house ‘when it was built’. Years ago detergents, soaps, disinfectants etc were not used as much, if at all. All of these affect the bacteria, which break down the solids in the tank. These tanks were not designed for these houses with recently installed power showers, washing machines, dishwashers.

Q. How much does it cost for an empty ?

This depends on the capacity of the septic tank or cesspool, and to a degree, how long since it has been since the last empty (we are charged more for disposal of heavy solids). If a tank is left too long before emptying, jetting may be needed to break up the solids and soakaway.
Getting you tank emptied every year is still cheaper than being connected to mains drainage.
Please call for a personalised quotation.

All Tanks Ltd can supply a vacuum tanker for septic tank emptying Reading.


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