Your Questions Answered About Septic Tanks

Posted by Callum Vallance-Poole, on February 22, 2021.

Graf UK Carat Septic Tank

If you’re in the market for a septic tank for your property, then you’re likely to have questions. 

Firstly, why might you need one and what does it do?

Septic tanks provide a treatment process to clean the black wastewater (sewage) from your home. Black water is the used water that comes from your toilets and dishwasher. It contains solid food particles and human waste. Septic tanks will also take the grey water from your property. This is the used water from your showers, baths and sinks. 

If you need to install a septic tank it is most likely because you cannot connect the wastewater from your property to a mains drainage network. This could be because there simply isn’t one – you may be in a remote area where existing drainage networks don’t reach – or it could be because the main drainage network close to you is already at maximum capacity and you’re therefore not allowed to connect to it. Either way, you’ve got to manage your own waste and have an individual system for your own property. 

A septic tank will first of all store all this wastewater coming from your house, usually into a primary chamber inside an underground tank. There are many types of tanks, but typically a septic tank is formed of 2 chambers to separate the waste inside. The black & grey water come into the primary chamber where the solids will sink to the bottom and the cleaner water will rise to the top. 

Once at the top, the cleaner water will flow into the second chamber, which will be largely filled with cleaner water and little to no solids. As the level of sewage within the tank fills up, the cleaner water will overflow through the outlet pipe, leaving the septic tank to go to a soakaway or drainage field (a drainage field is a network of perforated pipes buried underground, which allow the water from your septic tank to disperse into the ground, back into the water table). 

You may be wondering, how does a septic tank work?

Well, it’s almost as simple as the previous paragraph you just read. Incoming wastewater enters the septic tank, into the primary chamber, where the solids sink to the bottom of the tank and the cleaner water rises to the top. 

The cleaner water flows into the second chamber and slowly rises in this chamber as more wastewater enters the tank. Gradually reaching the outlet from the tank, where there is a pipe that takes the cleaner water out of the tank and into the drainage pipework installed as an overflow or suitable soakaway. The outlet from a septic tank must go to either a soakaway, which must have been sized correctly in accordance with the soil conditions and size of the system (i.e. the soil around the soakaway must be tested, by carrying out a percolation test, to determine the infiltration rate of the soil in order to calculate the size of the soakaway required), or into a drainage field as described above. 

Over time the septic tank will continue to fill and the cleaner water will flow out of the outlet and into the ground around it. As the solids build up in the primary chamber, they will reach a point when they have to be emptied out of the tank. This is very important. The length of time will be dependent on the size of the system and the usage. However, it is typically between 6 to 12 months between emptying on most systems. 

When it needs to be emptied you call a waste disposal company in your area – just Google ’Septic Tank Emptying’ and several companies will come up – and they will bring a vehicle that will suck out the wastewater from your tank so the whole process can start all over again. 

Another question you may be asking is; “what maintenance is involved?”

Thankfully, for any property owner who has a septic tank deal with the wastewater from their house, there is actually very little maintenance involved. The main thing to remember is to empty it when it is full. Once you do this, everything else happens without involvement from you or anyone else at all. It’s only if you start to notice issues, like bad smells or sewage getting anywhere that it’s not supposed to get to, that you would have to intervene and get a professional in to see what’s going wrong. In normal circumstances, most of the time, you won’t have to think about it at all. Everything happens automatically, underground, without anyone even realising. 

Which brings us to another question; “what things can go wrong and what to do if/when they do?”

If you notice that there is a bad smell coming from the tank, then there might be something wrong and you should take a look. By bad smell, this means that you notice a smell in the air when you’re several metres away from the tank, that wasn’t there before. [Not if you have the lid of the tank open with your head in it – it will smell from this close range, it’s sewage after all.] It’s more likely to be that you go outside your house and you can smell it in the air when you never could before. If this happens, then there may be something wrong. 

Most likely is that the tank is full and needs to be pumped out. You should check if the solids are up to the top of the tank and if so, arrange to get it emptied as soon as possible. 

If it’s not full and it’s only recently been emptied, then another potential problem is with the ventilation pipes for the system. Like all underground tanks, a septic tank needs to have a ventilation pipe for air to leave the tank as it fills up with wastewater. Just like when you fill your water bottle up, if the air had nowhere to go then it’s not going to fill with water! 

Now imagine, as the wastewater enters the tank, the air from the same tank leaves it through the vent pipe. Remembering that this is sewage water going into a tank, it’s fair to say that the air closest to it, is going to smell bad. This is normal. But it’s for this reason that it’s important that the opening of the ventilation pipe is not coming up above ground right inline with your nose! If the vent pipe is taken up higher, to the roof line of the house for example, then that smelly air that leaves the tank to allow the water to fill it, will only be smelt by the birds flying above your house and not by you or your guests. Sometimes these vent pipes can be forgotten or can be installed in an unsuitable place – this could be a reason why you’re noticing a bad smell from your system. 

Other potential problems are a blocked outlet from the tank, meaning the cleaner water isn’t getting through the drainage pipes or soaking away into the ground around the tank, therefore causing the wastewater in the tank to back-up into the incoming drainage pipe. Similar to this, there could be damage on any part of the pipework connecting to the septic tank and this may mean sewage is getting to places other than the tank. These sorts of problems will be hard to find and see by yourself. If you fear this could be the case then it’s definitely time to call in a qualified person who is familiar with underground wastewater tanks. They will have the equipment and experience necessary to get to the bottom of the issue and propose a solution. 

On this subject, one important thing to line up early in your position as ‘owner of a septic tank’ is to know who you’re going to call when you need help. There are lots of companies out there who install, commission, maintain and service septic tanks and wastewater treatment plants – find one close to you and have them as a person to call if you need help. 

One final question you may be wondering is what can go into your septic tank? Can you still use bleach? Do you need to add any additives? What can be flushed down the toilet? 

For this we would refer you to our “Bin it, Don’t Flush it” hand-out which provides a list of things you should not flush or pour down your toilet which will then find their way to your septic tank. With a septic tank, rather than a full wastewater treatment plant, you can still use bleach and cleaning products. The main risk of these with a full treatment plant is that they can kill or suppress the activity carried out by the bacteria that eat the waste and break it down to clean the water. As this is less of a process within a septic tank, it’s not as critical that you don’t use bleach. You also shouldn’t need to add any special additives to your septic tank as the whole process should work naturally, as described above. For other considerations, check out the “Bin it, Don’t flush it” document to be sure.

Marketing Coordinator - Based at our UK HQ in Banbury, Oxfordshire, Callum is responsible for promoting Water Management Systems, Attenuation Tanks, Treatment Plants, Rainwater Harvesting Systems and more!