Viewing a house that isn’t connected to the main sewer? Plenty of rural and semi-rural homes across the North West rely on a septic tank or a small sewage treatment plant, and many work perfectly well for years. But when you buy the house, you take on the system too. So what should you find out before you commit, what will our survey cover, and who answers the questions we can’t? This guide walks you through it, including how to choose between a Level 2 and a Level 3 survey.
- Find out exactly what type of system it is, where it is, and where the wastewater ends up.
- A home survey is a visual inspection. We don’t test drainage, septic tanks, or treatment plants.
- For the condition and performance of the system, you’ll need a drainage specialist.
- A Level 3 Survey (Building Survey) often suits the older, rural, or extended homes that tend to have private drainage.
- Ask for servicing records, plans, and any shared access details early, through your conveyancer.
Septic tank or treatment plant?
People often say “septic tank” to mean any underground sewage system, but the difference matters. A septic tank lets solids settle out, and the liquid then soaks away into the ground through a drainage field. A small sewage treatment plant goes further: it treats the wastewater, usually with powered parts, before it’s released.
A cesspool (or cesspit) is different again. It’s a sealed tank that simply stores everything until it’s emptied, so nothing is discharged at all. If the sales particulars or the seller’s forms mention one of these, make sure everyone is talking about the same thing.
The government’s guidance for owners of septic tanks and treatment plants explains the difference and sets out the general binding rules in England. These are the conditions that let most small household systems operate without a permit. Which rules apply depends on the type of system, where it discharges, and when it was installed.
Ask the seller for the make and model, the installation date, and any manual. If they don’t know, a drainage or maintenance company can usually identify it. A lid in the lawn and an emptying receipt are a start, but they don’t tell you how the whole system works.
Where does the wastewater go?
This is one of the most useful questions you can ask, and it’s worth asking early. Does the liquid soak into the ground through a drainage field, or does treated water flow into a ditch, stream, or other watercourse? Ask for a plan showing the tank, the pipe runs, and the discharge point, including anything beyond the garden boundary.
It matters because the rules differ. The Environment Agency’s rules for small sewage discharges to surface water say a septic tank mustn’t discharge straight into a watercourse. Where that’s happening, the system needs replacing or upgrading, and the guidance says responsibility for that work should be agreed as part of the sale.
That’s a question for a drainage specialist and your conveyancer, not for guesswork on a viewing. Please don’t decide the system is fine because a neighbour’s similar one has never caused trouble.
Choosing between a Level 2 and a Level 3 survey
Private drainage on its own doesn’t decide which survey you need. The whole house does. That said, septic tanks and treatment plants are most common in the kinds of homes where the choice often leans one way.
A Level 3 Survey (Building Survey) is usually the better fit for an older, rural, extended, or altered house, or one that’s been poorly maintained. It gives you a more detailed description of the building and any defects we find, with more discussion of likely causes and next steps. Our guide to the difference between a building survey and a homebuyer report explains the two levels side by side.
A Level 2 Survey (Homebuyer Report) can still suit a more modern, conventional house in reasonable condition that happens to have a treatment plant. It’s a thorough survey in its own right, not a basic one.
Whichever you choose, tell us about the private drainage when you ask for a quote. Let us know whether it’s shared, how old the house is, and whether it’s been extended. We’ll recommend the level that suits the property, and we’ll be clear about where specialist advice needs to take over.
What our survey does and doesn’t cover
Both survey levels are visual inspections of the building. The RICS description of the Level 3 survey makes clear that services are looked at visually, without specialist testing. That applies to private drainage too.
When we survey a house with a septic tank or treatment plant, we’ll note what we can see from safe positions: visible covers, signs of problems around the house, and anything that suggests you need further investigation. We won’t lift heavy or secured covers, go into chambers, test the system, or confirm that it meets environmental rules. We can’t tell you whether it’s big enough for the household or how well it’s performing.
For those questions, you’ll need a drainage specialist. Before you book one, ask what their visit will actually cover. Identifying the equipment is one thing. Checking its condition, capacity, discharge route, and servicing needs is another. A CCTV survey of the pipes can be really useful, but it may not assess the tank or plant at the end of them.
Read the paperwork as a story
Ask for everything the seller has: installation documents, servicing and emptying records, repair invoices, and any permits or letters from the Environment Agency. Then read them together, in date order. The pattern tells you more than the most recent receipt.
Check what each visit actually involved. Emptying a tank removes the sludge, but it isn’t a condition check. If a service report mentions a fault, look for the record showing it was fixed, rather than assuming a later invoice means it was.
For a treatment plant with pumps, blowers, or alarms, ask for the operating instructions and service schedule. You’ll need to know how to look after it once you move in. Please don’t press buttons or change settings on a viewing, though. Your conveyancer can request missing records through the sale, and if something can’t be found, note exactly what’s missing so the drainage specialist knows what still needs answering.
Shared systems and access
The tank might sit in your garden while the drainage field or outlet crosses a neighbour’s land, or several homes might share one system. Being able to walk to it today doesn’t mean you have the legal right to reach, use, and repair it once you own the house.
Ask your conveyancer to check the rights and responsibilities. For a shared system, find out who arranges servicing, how costs are split, and whether that’s written down anywhere. “We sort it out with next door” is a good starting point for questions, but it isn’t an agreement.
Think practically as well. Could an emptying tanker get close enough? Has a patio, extension, or new planting been built over part of the system? If covers are hidden or hard to reach, it may also limit what we can see, and our article on survey access and hidden areas explains how we record that.
Please keep well away from open, damaged, or loose covers, and never lean into a tank or chamber. If you spot a problem, tell the agent. Getting a closer look is a job for someone with the right equipment.
Think about how you’ll live there
A system that copes with one person may struggle with a busy family, and adding bedrooms can change what’s needed. Tell the drainage specialist how many people will live there and whether you’re planning to extend, so they can look at capacity properly.
A quiet viewing proves very little. An empty house puts almost no load on the system, and a dry spell won’t show how the drainage field copes after heavy rain. The evidence comes from the records, the plan, and the specialist’s findings. Our page on buying a home shows where these checks sit alongside the rest of your purchase.
If work is recommended, get a clear written scope and talk the implications through with your conveyancer and lender before you exchange. A quote in the seller’s file isn’t the same as finished work.
Questions about private drainage and surveys
Which survey should I book for a house with a septic tank?
It depends on the house. For an older, rural, or altered home, we’d usually recommend a Level 3 Survey (Building Survey). A Level 2 Survey (Homebuyer Report) can suit a newer, conventional house in reasonable condition. Tell us about the drainage and we’ll help you choose.
Will your survey tell me whether the septic tank works?
No. We’re not drainage specialists, and neither survey level tests the system. We’ll report what we can see from safe positions and flag anything that needs looking into. A drainage specialist can check its condition and how well it’s performing.
Does a recently installed treatment plant settle everything?
Not by itself. A newer plant is helpful, but it still needs to suit the house and the discharge point. Ask for the installation records, the manual, and any approvals, and let the specialist confirm how it’s set up.
What if the tank is on the neighbour’s land?
Raise it with your conveyancer before you go further. You’ll need to know that you have the rights to use it, reach it, and repair it. A friendly informal arrangement with the current owner won’t necessarily carry on after you move in.
Is an emptying invoice the same as a service record?
Not always. Emptying removes the sludge, while a service may also check the working parts. Read what each invoice says was done, and ask the contractor if it isn’t clear.
Do the same rules apply in Wales or Scotland?
No. This guide covers England. Wales, Scotland, and Northern Ireland have their own regulators and rules, so check the right authority’s guidance for a home there.
Send us the drainage details
If you’re buying a house with a septic tank or treatment plant in Liverpool or the North West, contact Trust Surveyors or call 0151 702 0123. Send us the address, the age of the house, and what you know about the system, and we’ll recommend a Level 2 or Level 3 survey and point you towards the drainage advice you’ll need alongside it.
