Shared Septic Tanks – What You Need to Know

Did you know that with some neighbours, you might not just share a border but also a shared septic tank, which is pretty common in the UK. Shared septic tanks can be just as efficient and just as useful as standalone septic systems that service one property. And as just as owning an individual septic tank, there are a few things you can do to ensure your shared septic tank is performing at its best.

terrace cottages using a shared septic tank

Shared Septic Tanks – Why Do Some Properties Share?

Shared septic tanks may be installed for a variety of reasons – for efficiency, minimising capital cost, reduced running-costs, space limitations or because they need to be built on third-party land. 

Shared septic tanks typically serve semi-detached or terraced properties with no access to mains sewage. These may be on rural properties or properties just too far from mains sewage lines. Most shared septic tanks serve two or three properties.  That said, on newer multi-property housing developments package sewage treatment plants are frequently installed in preference to individual septic systems.

While the majority of non-mains sewage properties have individual septic tanks and systems, shared tanks are widely used and have important legal and financial considerations to keep in mind.

How Many Properties Can One Shared Septic Tank Support?

A shared septic tank or sewage treatment plant can technically support an almost infinite number of properties! While you’d generally expect a shared tank to support just a few homes, the maximum service potential depends on the size of the system itself. 

Of course, the larger the tank (and the more homes it supports), the more complex things can become, both from a management and maintenance perspective. That is why, when purchasing or selling a property with a shared septic system, it’s important to establish who holds what rights to ownership, and what responsibilities there are for maintenance, pump-out and repair costs.

Where Are Shared Septic Tanks Normally Located?

Traditional septic tanks are normally found within property boundaries and that is also normally the case for shared tanks. Shared septic tanks don’t have to sit on property borderlines and typically they don’t.

In some cases, shared septic tank systems are built on third party land, providing each property equal access. 

When buying a property, it’s good practice to check whether a septic tank located on your premises will serve just your home or others close by too. Details should be available to you in the property’s deeds. Even so, your solicitor should request full details of its location, whether any other properties are connected to it, together with any recent pump-out and repair history.

While you are identifying who shares the septic tank, establish whether any drains are shared and which neighbours’ drains, shared or not, cross your land. 

Who is Responsible for a Shared Septic Tank?

Here’s where things get interesting. The responsibility of a shared septic tank is, fittingly, normally shared between households. That means even if the tank is on your property, it doesn’t all fall to you to maintain the system, paying for pump outs, maintenance and repairs.  

Neighbours who share a tank should have an agreement for managing the shared tank and its costs. It also means that, if you’re not the tank’s host, you may need to have permission to access the tank on your neighbour’s land occasionally.

This shared responsibility also means that if your tank causes any local pollution or nuisance, you and your neighbours will all be jointly accountable.

However, if such an agreement isn’t in place it’s worthwhile to draw-up a simple formal agreement between you and your neighbours and to have it approved by a qualified solicitor. It simply makes life better in the long run and life easier for all, should one of you choose to sell their property.

Who is Responsible for Paying for the Maintenance and Septic Tank Problems?

As well as holding some form of shared ownership rights, you’ll normally split the duties on maintenance, repair, ongoing costs, and replacement.  Equally and this has no bearing on the number of people living in each property, however, check your deeds – there have been a few rare occasions where a different agreement has been made in the past, that is binding.

How to Keep Your Shared Tank in Tip Top Condition?

The best way to keep a shared tank in great condition is to do your bit to prevent sludge build-up and blockages – only flush natural organic waste and toilet paper, and in addition, avoid chemicals. Change from chlorine-based toilet and household cleaners for septic tank safe options, which will keep your loo clean and maintain healthy tank bacteria.

Do also agree with your neighbours to top up your shared septic tank regularly with Muck Munchers. This will help to keep bacterial populations thriving and maximise waste digestion to minimise pump-out frequency. For larger installations, treating waste discharges from multiple properties with 12 or more people it will be more economical to use Mega Munchers, rather than Muck Munchers.

Common Problems with Shared Septic Tanks

One of the most common problems you’ll find with a shared septic tank is rising wastewater caused by blockages and crust layers. Both can arise through poor maintenance and inadequate waste digestion – and while you may be doing all you can to care for the septic tank, you can’t keep eyes on your neighbours’ waste disposal habits at all hours of the day. It is therefore wise to ensure that there is a common understanding between you and your neighbours.

Of course, achieving common agreement gets trickier the more homes there are that share a tank. The counter-side to this is that you’ll likely have a big enough tank to meet all connected households’ needs and being larger, it can be more forgiving. Regardless, it still means you’ll need to all play a part in keeping sludge levels low.

Drainage Problems and Shared Tanks

The question of drainage problems needs to be understood by the residents of all the connected houses. Common drainage problems arise when homes flush items or products that can kill bacteria or clog-up soakaways. 

You may also find that, if you have a neighbour hosting your shared tank, they may have tree roots growing through the tank soakaway without realising it. Soakaway damage can stop septic tanks from draining safely into the local ground, potentially causing broken drainage pipes, public health issues as well as slowing drainage to a halt. For more information on septic tank regulations regarding public health and environmental issues, read the General Binding Rules for England, Wales, Scotland and Northern Ireland at

Always make sure to regularly check your tank sludge levels. Agree with other users to inspect and the septic tank system, especially the sludge on a scheduled basis, at least a couple of times a year.

What to Do if You Experience a Problem with Shared Drainage?

If your shared septic tank is slow to drain or starts leaking, it’s the responsibility of all connected users to agree on a plan of action. You will most likely need to split the cost of any pumping or maintenance costs, and you should agree on who oversees call-outs and regular checks. In most cases, this will likely be the householder who hosts the tank on their land.

If you’re not the tank host and start noticing problems with drainage and flushing inside your home, take the time to meet with your neighbours. Ask the tank host to check the tank levels and whether othey are experiencing similar problems.

Ultimately, good communication is vital. A shared tank means working with your neighbours to ensure everyone can benefit from safe, reliable home sewage treatment. It’s more reason to draw up a shared septic tank agreement.

Shared Septic Tank Backing-Up

If your shared septic tank is backing-up and you’re doing all you can to keep your system clear of waste and sludge that could slow it down, it may be time to discuss maintenance with your neighbours.

It’s prudent to set up a maintenance schedule, decide who takes on which duties, and agree upon what not to flush. Careless flushing into a shared septic tank can impact other homes, drainage and plumbing – and if you there is no agreement, it has the potential to become a legal dispute. 

If the shared septic tank is backing up, you and other connected users may need to agree to pay for repairs. Before anything like that that happens, agree to add a bacterial treatment programme to your tank on a regular basis to maintain optimum waste digestion and minimise the chances of drainage back-ups.

What is a Shared Septic Tank Agreement?

A shared septic tank agreement is a written, legally binding document which details who is responsible for what aspects of maintaining a shared tank. It should detail how payments are made should repairs or pump-outs be required. 

For example, the written agreement may state that, as a tank host, you receive a set amount of money from your neighbours per year to cover routine costs. You should also detail what happens when maintenance needs arise, who agrees to take on which responsibilities maintaining the system and what happens in situations where there is disagreement between parties.

A comprehensive written agreement can help reduce potential disagreements over tank repair and maintenance. It’s important to establish what agreements are in place if you are planning to move to a new home with a shared tank. Talking to your potential new neighbours can also give you significant insight as to how they manage the tank on a day-to-day basis and provide you with re-assurance too.

Shared tanks are easy to look after if you communicate clearly with your fellow users and use Muck Munchers regularly to top up the bacteria to maintain a healthy septic system and soakaway.

For the past 8 years Muck Munchers have been mapping the geography of the UK’s Domestic Septic Tanks and Sewage Treatment Plants.
We would be delighted if you could spare a minute to take part in the Survey.
Do you have a Septic Tank or Sewage Treatment Plant?
Please tell us what type of Septic System you have?
Do you share your Septic System with a next door neighbour?
Do other properties in your local area have a Septic Tank or Sewage Treatment Plant?