The Cost to Empty a Septic Tank

All you need to know about emptying a septic tank including costs of materials, labour and time frames.

Cost to Empty a Septic Tank

What the job entails

People living in the city or suburban areas tend to take sewer systems for granted, but if you live in a rural location, then you will realise the importance of septic tanks. If there is no mains sewage, homes require a septic tank for baths, toilets and dishwashers to drain into. These tanks need emptying around once a year. Most contractors will need to drive a tanker onto your property so they will need unobstructed access between the septic tank and the parking area. The de-sludging or emptying service offered to customers with septic tanks usually includes the removal and treatment of around 1000 gallons of sludge. As part of the emptying process, the tank is also normally "backwashed" to remove any solids! This emptying service can be done as a "one-off" or more often as part of a regular maintenance contract.

Septic tanks use an outlet pipe that runs from into a drainage field or soak-away. A soakaway is a network of perforated or slotted pipes which allow the wastewater to percolate slowly into the ground without causing pollution. The septic tank separates out the waste into "scum", "separated wastewater" and "sludge". It's the separated waste water which runs into the soak-away system, the more solid yucky stuff stays in the tank which is why septic tanks need to be emptied out on a regular basis. If you don't empty your septic tank regularly then toilets will start taking longer to flush and you may even get stinking waste backing up to your home! The wrong kind of waste can then get into the soak-away system and pooling above ground, this creates an awful smell and can even pollute local water sources.

In terms of the cost to empty a septic tank, the size of your tank has a major effect as you would imagine. The bigger the septic tank, the more work to empty it out and flush the solids. But when choosing a tank, you need to remember that it's not just toilet and bathroom water, but water from washing machines, sinks and dishwashers too - so you need a tank with adequate capacity.

Smaller septic tanks are cheaper to install as they can often be above ground so no excavation costs, plus the tank itself is cheaper to buy, but smaller tanks will also require emptying more often, which can be expensive over the tank's lifetime. So larger tanks cost more to buy and install (usually they are underground) but are cheaper over the long term. The other benefit of a large septic tank is that a soak-away can be used for some of the waste-water to be filtered out so the tank is able to be emptied even less often. As long as septic tanks are emptied regularly and have been installed properly in the first place, they are largely problem free.

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The Cost to Empty a Septic Tank

A septic tank specialist emptying out your septic tank will be supplying their own specialist equipment to empty the tank and dispose of the contents safely. Usually they'll charge around £80-£300 per empty varying on the size and time it takes to clean. Depending on the size, this will usually only need doing once a year.

Below are some estimated costs to empty and clean out a septic tank:

Septic Tank Size Avg. Cost Duration
Small £100 30-45 mins
Medium £150 1 hour
Large £200 1-2 hours
Extra Large £300 2-3 hours

Cost Breakdown

Individual costs of cleaning a large septic tank - Total Cost: £200






Waste Removal


A septic tank is a chambered tank system into which retains sewage from a property flows and after a sufficient time the solids to form into sludge at the bottom of the tank where it is naturally broken down by bacteria. The remaining liquid then drains from the septic tank into a soak-away.
Like other sewage treatment systems, septic tanks are basically just a way of slowing the sewage to allow sufficient time for enzymes to break it up and reduce the contamination. The solids settle into a sludge whereas the liquid effluent on top is relatively low level in terms of contamination so can safely flow into a soak-away and then into a drainage field. Naturally-occurring microbes produce enzymes which help to break up the sludge.
Wastewater treatment plants usually have a supply of electricity to drive a small pump which aerates the waste water. Septic tanks have no electricity or moving parts, so they are cheaper, but the final effluent is not as clean so will require further treatment in a soak away.
Although much of the sludge is broken down, it's unlikely that all of it will disappear, so it tends to build up over time. So every year or so, the sludge needs to be taken out of the tank and the watery effluent which contains billions of the good microbes necessary for your tank to work properly is pumped back in. Strictly speaking, septic tanks are not really emptied but "desludged".
Yes, this top layer of scum is made up of fats, oils and greases. This scum will be broken down over time by microbes. The scum will not cause any problems unless it gets too thick, as it can then dry out and get hard, stopping air getting to the effluent which is needed for the microbes to do their job properly. So, if the scum is hard and dry, it's time to get a contractor in to desludge the tank.
Typically once a year, but as per the tank manufacturer's recommendations. There are also some bio-augmentation products which can decrease the build-up of sludge in your tank allowing you to desludge less often.
Essentially, this is the addition of useful bacteria. This helps the existing biological population or biomass to break down the solids in the septic tank more efficiently. If the tank environment is perfect, the biomass will be self-sustaining and new bacteria will not need to be added to replace those that die. But, the environment in a septic tank is rarely perfect so the regular addition of a bio-augmentation products helps to guarantee the right number and kinds of bacteria.
Probably, the biomass has died so some bacteria needs to be added to the septic tank immediately. The biomass can sometimes be killed off by cleaning products which are emptied down the sink or toilet.