Cesspit or Septic Tank Full or Overflowing? What to Do Before the Tanker Arrives

If your cesspit or septic tank is full or overflowing, stop all water use in the property straight away: no flushing, showers, baths, dishwasher or washing machine. That slows the rise while you arrange emptying. Then check whether the tank is genuinely full or whether a blocked pipe is making it look that way, because a tanker empties a tank but does not clear a blockage in the pipe leading to it. This page covers the first hour, what emergency emptying involves, and when it is safe to wait until the morning.

How to tell the tank is full rather than the pipe blocked

A full tank shows at the tank: a high-level alarm sounding, liquid near the top of the access lid, or sewage surfacing around the tank or soakage area. A blocked inlet pipe shows at the house: toilets and drains backing up while the tank itself is not full.

If you can safely lift the tank or chamber cover, look at the level. In a cesspit, liquid at or near the inlet pipe means it is full and needs emptying. In a septic tank, the liquid always sits at the outlet level, because it is designed to run on to a soakaway or drainage field, so a high level alone is normal. What is not normal is liquid above the outlet, sewage pooling on the ground over the drainage field, or wet, smelly patches that were not there before. If the tank level looks normal but the house is backing up, the pipe between the house and the tank is the problem, and that is a drain clearance job, not an emptying.

The first hour: cut the water going in

Nothing you can do reduces the level of a full tank, but you can stop adding to it. For a typical household, water use is the only thing that makes a full tank worse by the hour.

• Tell everyone in the property not to flush, shower, bath, or run appliances. Use a neighbour's facilities or a portable option if you need to.
• Divert any roof water or gutter downpipes that discharge into the same system, if you know they do.
• Do not add chemicals, bleach or so-called tank treatments. They do nothing for a full tank and can upset a septic tank's bacteria once it is back in use.
• Note when the alarm started or when you first saw the overflow. The engineer will ask, and it helps separate a full tank from a failing soakaway.

Keep people and pets away from surfacing sewage

Raw sewage on the ground is a health risk, so the second job is to keep everyone away from it until the tank is emptied and the area cleaned.

Keep children and pets off the affected part of the garden. Do not try to shovel or hose it away; hosing adds water and spreads it. If it is running towards a watercourse, a ditch or a neighbour's land, say so when you call, because it changes the urgency and you may need to tell the Environment Agency. Wash hands thoroughly after touching anything it has reached, and keep shoes worn in the garden outside.

What an emergency emptying involves

A tanker parks within hose reach of the tank, the engineer lifts the cover, and the contents are pumped out through a suction hose into the vehicle. For most domestic tanks the pumping itself is a short part of the visit; access usually takes longer.

The practical things that decide how the job goes are distance and access. A suction hose has a working length, so a tank at the far end of a long garden, behind a locked gate or below a steep slope needs planning. Tell us on the phone roughly how far the tank is from where a vehicle can park, whether there is a gate or steps, and whether you know the tank's size. After emptying, the engineer checks the inlet and outlet while the tank is empty, which is the easiest time to see a blocked inlet or a damaged baffle. The waste goes to a licensed treatment site, and you should receive a waste transfer note. More detail is on the septic tank and cesspit emptying page.

Why an overflowing septic tank is not always a full one

A septic tank that overflows soon after it was emptied usually has a problem downstream: a blocked outlet, a failed soakaway or a saturated drainage field. Emptying it again buys time but does not fix it.

A septic tank separates solids and lets the settled liquid flow out to the ground. If that ground stops accepting water, because of silt, roots, compaction or a high water table after long rain, the liquid backs up and the tank looks full. Cesspits are different: they have no outlet at all, so a cesspit that fills faster than usual is almost always a water-use problem, such as a leaking toilet cistern running into it or roof water that should not be connected. Our septic tank and soakaway guide explains how the drainage field side works.

Does it need doing tonight?

If sewage is backing up inside, surfacing near the house, or running off your land, yes. If an alarm has sounded but nothing is overflowing and you can stop using water until the morning, it can usually wait.

Most high-level alarms trigger with some capacity left, precisely so that you have time to book. If you can manage without water overnight, a standard-hours visit costs less than a night one for the same emptying. We charge by time band, 7am to 5pm, 5pm to midnight and midnight to 7am, and agree the band figure on the phone before a tanker travels. The bands are listed on the pricing page.

After the tanker leaves

Once the tank is empty, find out why it filled when it did. A tank that reached capacity on its normal schedule just needs booking in earlier next time; one that filled early needs investigating.

Check toilets for a cistern that runs continuously, look for a dripping outside tap or leaking pipe that drains into the system, and confirm no rainwater downpipes feed the tank. For a septic tank that overflowed, ask for the outlet and drainage field to be looked at before assuming the next emptying will fix it. Keep the waste transfer note with your property records.