Septic Tank Not Draining Properly? Here's What It Means

A septic tank that isn't draining is a problem you can't ignore. Slow sinks, bad smells and soggy ground all point to a system in trouble.

This guide explains the warning signs, the common causes and what to do next.

Signs your septic tank is not draining properly

Look out for these:

• Sinks, baths and showers that drain slowly
• Toilets that flush weakly or gurgle
• Bad smells in the house or around the tank
• Wet, soggy or very green patches on the lawn
• Sewage backing up into drains
• Standing water over the drainage field

One sign on its own may be minor. Two or more together mean you should act.

What causes a septic tank to stop draining

1. The tank is full

This is the most common cause. Sludge builds up at the bottom of the tank. When it gets too high, solids flow out and the system backs up. Tanks need emptying at least once a year. Read how often a septic tank needs emptying in our septic tank emptying guide.

2. The drainage field is blocked or failing

Liquid leaves the tank and soaks into the ground through the drainage field. If the soil clogs with solids or grease, water has nowhere to go. It rises to the surface or backs up into the house. A blocked field is serious, and it gets worse the longer you leave it.

3. A blocked pipe

The pipe between your house and the tank, or the outlet pipe, can block. Causes include grease, wipes, tree roots and collapsed pipework. A blocked pipe is quicker and cheaper to fix than a failed field.

4. Heavy rain and high water

Wet ground can't take more water. After heavy rain, the field may flood and the tank may not drain. Our post on why UK drains are struggling with this year's rainfall explains why this is happening more often.

5. Damage to the tank or baffles

Cracks, broken baffles or a damaged outlet let solids escape. That speeds up the blocking of the drainage field.

6. Too much water or the wrong products

Lots of laundry in one day, strong bleach, wipes and cooking fat all upset the system. They stop the bacteria working and fill the tank faster.

7. A treatment plant fault

If you have a small treatment plant rather than a septic tank, a failed pump, blower or control panel can stop it working. Check for alarms and unusual noise.

What to do now

1. Cut down water use. Delay laundry and long showers.
2. Don't use drain chemicals. They kill the helpful bacteria and rarely fix the cause.
3. Check when it was last emptied. If it was over a year ago, book an emptying.
4. Look at the ground. Note any wet patches or smells and where they are.
5. Call a specialist. The longer you leave it, the more expensive the repair.

If sewage is backing up into your home, treat it as an emergency. Call us right away.

How we fix it

Every job starts with working out the cause. Then we fix that, not just the symptom.

• Septic tank emptying clears a full tank
• CCTV drain surveys show blocked or broken pipework
• Drainage field installation and repair deals with a failing field
• Percolation testing checks the ground can take the water
• Septic tank and treatment plant servicing keeps the system working
• Septic tank replacement if the system has reached the end of its life
• Emergency sewage removal if sewage is already in your home or garden

We offer a free site survey before any quote. Our emergency line is open 24/7, 365 days a year, including bank holidays.

How to stop it happening again

• Empty the tank at least once a year
• Don't flush wipes, nappies or fat
• Spread laundry through the week
• Keep trees and large shrubs away from the drainage field
• Don't park or drive over the tank or field
• Keep service records. Our post on septic tank compliance explains why they matter

Get your septic tank looked at

If your septic tank isn't draining, don't wait for it to get worse. Call us on 0203 870 1067, email contactus@icedrainage.co.uk or get a quote today.

Related reading: septic tank and treatment plant services.