How to unblock a drain
More advice on blocked drains
- A set of drain rods will set you back about £20 from your local DIY store
- Solidified fat is the most common cause of blocked drains
- To clean a pipe add bleach then pour on oiling water
How will I know if my drain is blocked?
You’ll know if your drain is blocked because waste water won’t drain, toilet water won’t flush away and drain, or manhole covers may start to overflow - or you may be able to smell the problem. If it’s just a sink that’s blocked, read our advice on how to clear it.
How do I locate the blockage?
First lift the drain or manhole cover nearest to your house, using either a manhole key, a large screwdriver or spade to lever it up. Manhole covers can be very heavy, so get someone to help you lift it, and be very careful not to trap fingers or your feet underneath, while lifting.
A safe way to do it is have one person lift, and then another slide a thick wooden batten across the hole, and under the cover. Then you can both slide the cover aside safely.
If the chamber is empty the blockage is somewhere in the soil pipe from the house to the manhole. If there is water in the chamber, the blockage is either located further down the pipe towards the mains sewer or in the chamber itself.
If your home is a long way from the mains sewer, keep checking all the covers between the full manhole and sewer until you find an empty one. The pipe between the last full manhole and the empty one will have the blockage. (Unless there is more than one, then you will have to clear the blockages one at at time.)
How do I clear the blockage?
Screw your first two drain rods together, and insert the plunger into the blocked pipe from the empty chamber. Keep adding drain rods as you go until you feel the blockage, turning the rods in a clockwise direction as you go. (Don’t turn them in an anticlockwise direction the rod joints will unscrew.)
Push and pull until you feel the blockage start to give way. If it won’t, then remove the rods and try the corkscrew attachment instead of the plunger. If this is successful then remove the drain rods and turn on your hot tap in the house and flush through with a detergent to remove any fat build up and lingering debris.
In older properties, you may have what is called an Interceptor Chamber, and clearing these needs a different approach. Interceptor chamber manholes are usually rectangular and the walls are built of brick. This chamber is usually the last one before the mains sewer.
The chamber has two pipes out of it heading towards the sewer, their entrances one above the other. The lower pipe is basically a U-bend, and stays filled with water to stop fumes coming back up from the sewer.
The pipe above usually has a lid on it. The idea is that this section of pipe is only used to empty the manhole when the U-bend is blocked, and it is normally covered with the lid… sometimes called a tea-pot lid.
So, to clear this chamber of waste, feel about for the teapot lid - it sometimes has a chain, too – with a stick or one of the drain rods, then pull the lid out of the pipe, and all the waste in the manhole should drain away.
Now you can see what you are doing, use the drain rods to try and clear the bottom drain with the U-bend. If this works, then run your home's hot water and use detergent to flush the system though. Then replace the lid on the top drain, replace the manhole cover and your problem should be solved.
What do I do if the blockage won’t clear?
It’s at this point that you check your insurance policy to see if you’re covered. If not, call in the professionals! Be warned that some companies advertise a cheaper job rate then charge extra if they use a high pressure jet. Expect to pay £80-£100 plus VAT, more if you’re in London or if it’s a weekend. If it transpires that it’s tree roots or a collapsed drain causing the blockage expect to pay a lot more. From the 1st October 2011, homeowners are only liable for the drains within the boundary of their own property and those that are not shared. Liability for all other pipework rests with the utility company who should be contacted.
How do I prevent my drains getting blocked?
It all comes down to proper disposal of waste. The following should not be flushed down the drain:
A good (cheap) buy is a drain tidy to cover the base of your external pipes and prevent leaves and other debris falling down the drain.
For more troubleshooting plumbing advice read:
Problems with toilets
How to fix a dripping tap
How to fix a burst pipe