Option one
Repair what's there
- Can suit when
- The tank is sound, the right size, and drains somewhere acceptable, with a limited fault such as a broken pipe.
- Bear in mind
- A repair won't fix a system that drains somewhere it shouldn't or is too small.
Septic Tank Replacement
When a septic tank has failed, is past its working life, or no longer meets the rules, replacement starts with understanding the whole system. The right answer might be a new tank and drainage field, a treatment plant, or a repair.
- Assessment before any recommendation
- Written quote that says what's included
- Building Regulations and permits explained
- Ground put back as agreed
Why replace
Why people look at replacing a septic tank
Some systems fail suddenly. More often, problems build up over years until the tank or the drainage field can't cope. These are the reasons we hear most.
The usual first signs are drains that run slowly, gurgle or back up, and smells around the tank or the garden. Ground over the drainage field that stays wet, mushy or unusually green is another, as is needing the tank emptied more and more often.
Some reasons have nothing to do with how it performs. An older brick or single-chamber tank may be cracked or leaking. The tank may drain straight into a ditch, stream or river, which the rules no longer allow. A survey for a sale may have flagged it, or an extension may mean more people using it than it was built for.
The tank isn't always the problem. A blocked or waterlogged drainage field causes many of the same signs (see the warning signs). That's why we look at the whole system before anything is replaced.
The assessment
What we check first
The assessment builds a picture of your system and your site, so the recommendation fits your property rather than a standard package.
The existing tank
Type, age, condition, size, and whether it suits how many people live there.
Pipework and levels
The pipes in and out, how deep they run, and whether gravity can do the work.
Where it drains
A drainage field, a pipe to a watercourse, or somewhere nobody is sure about.
Ground conditions
How the soil drains, the water table, and whether ground testing is needed.
Access
Routes for a digger now and an emptying tanker later. Gateways, slopes and soft ground all matter.
Power and position
Electricity for a treatment plant, and distances from the house, boundaries and water.
Your options
Repair, replace, upgrade, or something else
A replacement septic tank isn't always the answer, and a septic tank upgrade to a treatment plant can be the better long-term choice. These are the main routes, and the assessment decides between them.
Option two
New septic tank and drainage field
- Can suit when
- The ground drains well and there's room for a correctly sized drainage field.
- Bear in mind
- A new tank on an old, failed drainage field soon has the same problems.
Option three
- Can suit when
- Space or ground conditions are limited, or a watercourse is the only realistic outlet.
- Bear in mind
- Needs a permanent electricity supply and regular servicing as well as emptying.
Option four
Another arrangement
- Can suit when
- A mains sewer connection has become possible, or the site rules out the usual options.
- Bear in mind
- Sealed holding tanks are usually a last resort because of the emptying costs.
The process
How a replacement usually runs
This is the general shape of a project. The exact method depends on your site, the system chosen and the approvals needed.
- 1
Assess the system and the property
What's there, how the property is used, and what's going wrong.
- 2
Investigate the site
Ground testing where needed, routes for machinery, and where the wastewater can go.
- 3
Recommend and quote
A written recommendation, and a quote that says what's included and what isn't.
- 4
Sort the approvals
Building Regulations, any environmental permit, and planning where it applies.
- 5
Install, and deal with the old system
The old tank is emptied, then removed, filled or made safe as agreed.
- 6
Test, put the ground back, hand over
Checks suited to the system, reinstatement as agreed, and the paperwork handed over.
Cost
What affects the price
We don't publish standard prices, because two replacements rarely cost the same. These are the things that move the figure most. Read the full cost guide.
The system you need
Septic tank or treatment plant, and its size.
Ground conditions
Test results decide the drainage field size, or whether one works at all.
Depth and levels
Deeper digs, or a pump where the levels don't fall naturally.
Access
Tight gateways, slopes or soft ground mean smaller machines and longer on site.
Distance to the outlet
Longer pipe runs and new drainage fields add materials and digging.
The old system
Emptying, removing, filling or making safe the existing tank.
Electricity supply
Running power to a treatment plant if there's no supply nearby.
Putting it back
Lawn, gravel, paving or concrete over the work area.
On site
Disruption, access and putting the garden back
Replacing a septic system is groundwork. Knowing what to expect makes it easier to plan around.
During the work
- A digger and dumper on site, with soil stored nearby
- A period when the drains can't be used, so ask about temporary arrangements
- Deliveries of the tank, gravel and backfill
- Some noise and vehicle movements during working hours
Afterwards
- Agree in writing what reinstatement includes before work starts
- Ground over the dig can settle and need topping up
- Turf, seeding and paving are often priced separately
- Access covers stay visible and reachable for emptying
Afterwards
Handover and looking after it
A good handover leaves you knowing what's in the ground and how to care for it. Keep the paperwork with the house, because a future buyer will ask for it.
You should come away with the product details and manufacturer's documents, a plan showing where the tank or plant and the drainage field sit, and any commissioning or test records. Where Building Regulations apply, there's completion paperwork too. You'll also get guidance on emptying, servicing and what not to put down the drains.
How often a system needs emptying or servicing depends on the unit, its size and how many people use it. Follow the manufacturer's guidance.
Questions
Septic tank replacement questions
Can my existing septic tank be repaired instead?
Sometimes. If the tank is sound, the right size and drains somewhere acceptable, a targeted repair may be enough. The assessment will tell you whether a repair is sensible or just a delay.
Do I need permission to replace a septic tank?
A replacement normally needs Building Regulations approval. If the new system can't meet the general binding rules, an environmental permit may be needed, and planning can apply in some cases. Your quote should say which apply.
How much does a septic tank replacement cost?
It depends on the system you need, ground conditions, access, the distance to the drainage field or outlet, and how the garden is put back. We don't quote a figure without seeing the site, but your quote will break down each of these so you can compare it fairly.
Can I upgrade to a treatment plant instead?
Often, yes. Upgrading to a domestic sewage treatment plant is common where a septic tank drains into a ditch or stream, or where the ground won't take a new drainage field. Treatment plants need electricity and regular servicing.
How long does a replacement take?
It depends on the system, the ground, access, the weather and approvals. You'll get an expected timescale for your site after the assessment, not a standard figure that may not apply.
Can I use my toilets during the work?
There's usually a period when the drains can't be used while the old system is disconnected and the new one connected. Ask how long that's likely to be and what temporary arrangements are possible.
What happens to the old tank?
It's emptied by a licensed waste carrier first. Then it's removed, broken down and filled, or made safe in place, depending on the site and what's agreed.
Not sure whether you need a replacement?
Tell us what you've noticed. Photos of the access covers or the area around the system help if you have them, but they're optional. We'll tell you what's worth looking at first.
Thinking about replacing your septic tank?
Tell us what's happening and roughly where you are. No need to know what type of system you have.