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Buying a house with a septic tank

Buying a house with a Septic tank, Cesspit or Sewage Treatment Plant

A guide for those buying a new home that is not on mains drainage. To arrange a home buyers survey for the new property please call us on 0800 3101092 or via our contact form.

Buying a house with a Septic Tank, Cesspit or Sewage Treatment Plant

Septic Tank Survey Reviews
Call the experts on 0800 3101092 to arrange a Survey or contact us here.  

Buying a property with a Septic Tank, what to consider

  • Unlike mains sewage you will have certain legal responsibilities when owning a house with a small sewage discharge. You need to understand what these responsibilities are and the legal framework that exists.
  • What types of off-main solutions are there and what does it mean?

  • What are the costs of running each system?

  • How will owning a property with off-mains drainage affect you?

  • What are the risks of owning an off-mains system
  • What should I ask before buying the property?

Septic Tank Survey Reviews

An overview of your responsibilities and the associated legal framework

If you are buying your first house without a connection to a mains sewer then this guide will be indispensable for you. It will also be useful for those who have not owned such a property for some time. There has been and continues to be significant regulation change in this sphere and it is important you understand your responsibilities. There is literally a ton of stuff to understand, especially if you are new to it.

Firstly you need to have a working knowledge of the associated regulation. On the 1st of January 2015, the General Binding Rules for small sewage discharges came into law. If your system does not adhere to the General Binding Rules and you do not have a Permit the discharge is illegal. The responsibility for compliance is with the operator, so you. The Environment Agency (EA) has recently issued updated guidance for new home owners, which gives you a grace period of 12 months from moving into your new home to ensure your system is compliant.  

 It is illegal to discharge effluent to either ground or surface without a Permit issued by the Environment Agency or by adhering to the General Binding Rules.

Please read our General Binding Rule Guide before starting.

If you are buying a house you should consider having the drainage system surveyed before you move in. Our surveys will tell you whether the system complies with the General Binding Rules as well the general condition of the system. A new Sewage Treatment Plant for an average size suburban house can cost between £10k and £18k. Please our survey page. A full survey with a written report costs £600, which compared to the potential costs involved is money well spent. 

What types of Small Sewage Discharge solutions are there and what does it mean?

Off drainage or private drainage means that the effluent your household produces is collected on your property. The effluent is not taken care of by someone else it is your responsibility.

The effluent almost exclusively flows into an underground tank of varying size and construction. The three main types of the tank are a Cesspit, Septic Tank and Sewage Treatment Plant.


 A Cesspit has no outflow it is a tank that simply collects your effluent. These types of tanks require regular emptying. Please see out Cesspit guide.

Septic Tank:

A Septic Tank is a tank that has a dividing wall. The wall allows liquid effluent to pass through but stops the solids. The liquid effluent then passes into a drainage field where it is treated or into surface water. From the 1st of January 2020 a septic tank can no longer discharge to Surface Water the discharge will become illegal. 

Treatment only occurs if the drainage field is constructed properly. It is the owner’s responsibility to ensure that the drainage field is constructed and is working in line with the General Binding Rules. My estimate is that 90% of Septic Tank owners discharging to the ground do not have a compliant Drainage Field.

Per the General Binding Rules, any non-compliant Drainage Filed needed to be upgraded as of the 1st of January 2015. If you discharge to ground you have to have your tank emptied annually and keep the evidence of this. Failure to comply again means you have an illegal discharge. Please see our Septic tank page for more detailed information.

Sewage Treatment Plant also known as a wastewater system or packaged treatment plant:

A Sewage Treatment Plant is a tank that treats the effluent internally and discharges effluent to a certain standard of cleanliness. The Standards are clearly set and all tanks must adhere to them. This means as well as an annual empty you have to also have your tank serviced and the effluent quality checked.  Please our guide to buying a Sewage Treatment Plant and Servicing for more information.

A properly functioning Sewage Treatment Plant can discharge to surface water. If discharging to ground you have more options than with a Septic Tank as you are effectively discharging clean water. 


What are the pros and cons of each system?

Cesspit Pros & Cons

Cesspits are very simple but as they do not have a discharge the cost of regularly emptying them can be large. Again please see our Cesspit guide which looks at calculating this annual cost. Effectively a person is estimated to produce 150 litres of discharge a day. A 4,500L empty costs about £150. So a single person would need an empty every 30days. Therefore an annual cost of around £2k, for one person.

Septic Tank Pros & Cons

A Septic Tank is an effective system, however, when buying a house it is likely that the system will be old and near the end of its life. Many tanks have leaks and are no longer structurally sound. Septic Tanks have rarely been maintained in line with the General Binding Rules; therefore the soakaways are normally compromised.

The Soakaway on a Septic Tank will fail eventually it is inevitable. If the Septic Tank discharges to a watercourse or ditch it is illegal. If it discharges to the ground then in 90% of cases the discharge is also outside of the General Binding Rules. In this case, a permit to discharge or a new drainage field is required. Many properties do not have the conditions to accommodate a new drainage field in line with the relevant building regulations. It is likely that the rules around Septic Tank discharges will become more stringent in the future.

Sewage treatment Plant Pros and Cons

Sewage Treatment Plants are more versatile than the other systems and as the discharge is clean the system is far less likely to fall foul of any future legislation change. The plants are more expensive to maintain as there are parts that fail, this is especially the case with certain brands. Again please see our buying guide. Overall I would prefer to buy a house with a good Sewage Treatment Plant. There are however several shocking brands with dreadful support, worthless warranties and very expensive parts.  

What are the costs of running each system?

The annual cost of running and replacing a Cesspit

The cost of running and owning a Cesspit will be around £5k per year. A replacement installation will be around £5k to £6k + VAT.

The annual cost of running and replacing a Septic Tank

The cost of running a Septic Tank will be around £150 per year. A replacement drainage field, if conditions allow (which in many cases they will not) ranges from £3k to £6k + VAT for a normal-sized property. A replacement Septic Tank for a normal-sized house with good conditions and access will cost between £5k and £7k + VAT.

The annual cost of running and replacing a Sewage Treatment Plant

 The cost of running a Sewage Treatment Plant is around £300 to £400. This includes service and an empty, which you are legally obliged to carry out. Please see our servicing page for more information. A new Sewage Treatment Plant discharging to surface water will cost between £8k and £10k + VAT for a 4-bed house with good access and ground conditions. A new Sewage Treatment Plant discharging to the ground will cost between £9k to £13k for a 4-bed house with good access and ground conditions.

In summary, I have found, amortising the initial investment cost, that the cost of living off sewer is cheaper than living on sewer. This is mainly because the on-grid sewage providers are monopoly providers that are not adequately regulated.

How will owning a property with off-mains drainage affect you?

The main impact is that you are responsible for ensuring the system is compliant with the General Binding Rules or conditions of your discharge permit. Simply you will need to arrange an annual inspection, service and empty. Please see our servicing page to arrange or for more information.

You will also be responsible for fixing any problems. We would recommend that you get this covered by your household insurance.

What are the risks of owning an off-mains system

There are three main risks to owning an off-mains system.

  1. You breach the General Binding Rules and are fined by the Environment Agency and forced to rectify the issue.
  2. An element of your system fails. This could lead to a costly repair and an emergency call out. In the interim, you will not be able to use your facilities.
  3. Legislation changes and you have not kept up to date with these changes.

All of the risks can be mitigated by employing a professional servicing company and taking out the relevant insurance.

What should I ask before buying the property?

The seller is legally obliged to provide you with the following in writing:

  1. A description of the treatment system and drainage system
  2. The location of the main parts of the treatment system, drainage system and discharge point
  3. Details of any changes made to the treatment system and drainage system
  4. Details of how the treatment system and drainage system should be maintained, and the maintenance manual.
  5. Maintenance and emptying records.

Also, ask them if there has been any problem with the system. Also, look to get a professional survey undertaken.

Want to learn more?

We have a large collection of articles containing the answer to all of your questions. Check out our Blog Page 

Our Core Services: The Sewage Treatment expert Installers

On the 1st January 2020, all Septic Tanks that discharge to a Stream, Watercourse or Drainage Ditch will become illegal and will require replacing with a Sewage Treatment Plant. Please see here for more details.

Expert wastewater treatment engineers who specialise in Septic Tank and Soakaway replacements as well as Sewage Treatment Installations. We are based in the New Forest, Hampshire but operate across the South Coast as well as Wiltshire, Somerset, Devon, Sussex, Surrey, Oxfordshire, and Berkshire.

The Home of Septic tank and private drainage system solutions. 

Based in the New Forest, Hampshire on the border with Dorset and Wiltshire we operate an expert team of off-mains drainage specialists. This encompasses Septic Tank, Soakaway and drainage system problems, installations, blockages, and servicing. In addition, any issues relating to cesspits and sewage treatment plants.

Homeseptic offers high quality, professional advice, repairs and installation for all aspects of effluent cleansing and disposal across the south of England. Whether you’re looking for septic tank installation, sewerage treatment plants or systems, piping or soakaway solutions, Homeseptic employs only the most competent engineers in the drainage and treatment industry and knows exactly which solutions suit each property.

We only install and offer quality systems we believe in, from suppliers we know and trust.

New Forest Philosophy

As we have said Homeseptic is based in the New Forest. A great location in between the cities of Southampton, Salisbury and Bournemouth. We are a group of good friends who grew up together in the area.  Individually we all have grown tired of the way other Drainage firms are run. As a result, this is why we set up Homeseptic. If you want to know more please check out our About Page

We want to actually put the customer first and turn up to do a great job that we can be proud of. Unfortunately, this is not the case in the market, with most companies pressuring their workers to sell unnecessary works on a visit. Due to this, we offer upfront quotations with any variations discussed before we start work.

We are honest hard working professionals, which we hope you will agree with. As a result, it will certainly not turn up in flash sales vehicles and give you a load of chat and then do a terrible job. Our team will come with the job in mind and the aim of giving you the best value we can in order to facilitate a quality installation. 

We cover all of Hampshire, West Sussex, Dorset, Somerset, and Wiltshire. Please get in touch and see what you think.

Homeseptic Ltd. is rated 4.8 out of 5 based on 28

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Buying a house with a Septic tank, Cesspit or sewage treatment plant
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Buying a house with a Septic tank, Cesspit or sewage treatment plant
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