How your septic tank works - the ultimate guide!

Knowing about how a septic tank works isn’t the kind of knowledge that will make you a hit on the dinner party circuit overnight. But in spite of the unpleasant subject matter, if your property has a septic tank then you really should know what’s going on underground.

If you have any septic tank problems, a little knowledge will go a long way – and you might feel a little less daunted if you hear the inevitable sharp intake of breath when a drainage person lifts a lid and peers in.

So, bear with me for a while and I will try to explain it all as best I can. To help things along, you can also watch our video illustration (don’t worry, it’s an illustration rather than a real septic tank full up of stuff that might put you off your lunch).

Where is a septic tank usually located?

As a general rule, a septic tank is under the ground within the boundary of your property. Sometimes it might be located in land not owned by yourself – and this is when things can get tricky.

If your property has a drainage system on someone else’s land, you should have an `easement’ in place which is a legal right to have your system on their land, and to be able to access it for maintenance and repair.

You should find information relating to any drainage easement in your property’s deeds. You might have a legal right to access someone else’s land to fix your septic tank if it stops working – but our best advice is to do whatever possible to stay on friendly terms with them in case of any issues.

At UKDP we have seen many situations where a feud over septic tank problems escalates to the point that damaged systems can’t be fixed without lengthy (and costly) legal arguments over access. So, avoid all that by sending regular Christmas cards to your neighbouring landowner while your system is still ticking along nicely. It’ll pay dividends when you need their help in getting it fixed!

If you’re not sure where your property’s septic tank is at all, the location can be identified above ground by two or three manhole covers situated quite close to one another. These give access for regular septic tank emptying and septic tank inspections.

How does the septic tank work?

Here’s the video I mentioned earlier, take a look if you have a few minutes to spare.

Once you’ve flushed your loo or emptied your sink, the waste water leaves your property through the drainage pipes to your septic tank, and will usually pass through a number of inspection chambers or manholes.

Here comes the technical bit, brace yourself.

There are a number of different types of septic tanks, but the most common types are constructed of brick or GRP (Glass Reinforced Plastic) and are divided into two chambers. Each chamber is equipped with an inlet and an outlet pipe, known as a T-piece or dip pipe. Once the waste water reaches the level of the outlet pipe in the first chamber, it will overflow into the second chamber.

The inlet and outlet dip pipes play a vital role in retaining the solids in the waste water long enough so that they can be broken down by bacteria within the tank. As the first chamber fills up, the vertical section of the dip pipe prevents the fat and floating solids in the waste water from making its way to the next chamber.

When the waste water settles in the first chamber, the solids in the water break down and separate into 3 distinct zones or layers:

  • The top layer is made up of less dense matter – fats, oils and solids that have not yet broken down, also known as the crust (if that doesn’t put you off your sandwich, I don’t know what will)
  • The second layer is mostly dirty water without any solids remaining, and it is this water which passes out of the septic tank and into the soakaway system
  • The bottom layer is known as sludge (mmmm), and consists largely of more dense waste that builds up slowly over time. This and the top layer of crust is what must be removed during a routine septic tank emptying.

This separation process will repeat itself depending on how many chambers your septic tank has. The liquid leaves the tank and makes its way in to the soakaway system.

A waste water soakaway is the section of a drainage system that follows on from a septic tank or sewage treatment plant. The purpose of a soakaway system is to allow the liquid waste that has left the septic tank to percolate through the soils surrounding the pipework – the soakaway pipework is often perforated or slotted to enable this to happen. The process of the liquid waste percolating through the particles in the soil provides a form of treatment of the waste, and it is then safely dispersed into the surrounding sub soils.

If you’re still reading, well done, you are now knowledgeable in the ways of septic tanks and you can safely remove that one from your bucket list.

How to keep your septic tank working

Septic tanks and the soakaway systems they connect to won’t last a lifetime, but with a bit of care and attention you can make sure that you get as many years of trouble free drainage for your property as possible. Following these simple tips would be a good place to start:

1. Be careful what you flush down the loo or put down the sink

The waste water entering your septic tank should only include waste from your property’s toilets, showers, sinks and kitchen appliances. Septic tanks aren’t designed to take rain water or surface water, this will quickly overload them and stop them working properly. You should never allow the following to pass into a septic tank by flushing down toilets, as they are likely to quickly cause problems:

  • Sanitary products
  • Disposable nappies
  • Face wipes

(Please note that I haven’t added anything like goldfish or small plastic animals to this list, although anyone with small children may consider those just as likely as any of the above to be flushed down the loo)

Similarly, you should be very careful with what you pour down the sink, in particular:

  • Fats or cooking oil should be disposed of separately and never poured down the sink - this in particular can cause soakaway problems as it can prevent the soil surrounding your soakaway system from being able to absorb the waste water effectively
  • Anti-bacterial products such as kitchen cleaners and handwashes should be avoided as they can kill off the `good’ bacteria in your septic tank which helps to provide a basic level of treatment to the waste water that goes into it

2. Get your septic tank emptied regularly

Ensuring that your septic tank is emptied (also known as `de-sludged’, another lovely drainage term for you there) regularly is important in ensuring that it can work properly. A tanker will attend your property and will remove the solids and waste water from your tank.

How often you will need this to happen depends on a number of different factors, but in general most septic tanks need to be emptied each year. If you’re not sure, just ask a local tanker company to give you advice.

3. Keep your eye out for any septic tank problems

The company that empties your septic tank should let you know if they spot any problems with the drainage system. Don’t just put this to the back of your mind, which of course is tempting to do if it’s not started to affect you yet. You may also notice:

  • dirty water pooling above the ground where your septic tank or soakaway system is
  • your toilets flushing slowly or overflowing
  • your septic tank filling up more quickly and needing to be emptied much more frequently than usual

If you notice any of these problems, it is important to get a septic tank inspection carried out as quickly as possible to identify what’s causing the problems, and to ensure that action can be taken before they get any worse.

The team at UKDP can offer you expert advice and guidance on any septic tank or soakaway problems, so call us today on 01628 788600 or contact us here. We’re a friendly bunch and we’ll do our best to help.

0800 028 9903