Blocked Drains and Waste: Causes, Fixes and When to Call the Water Company

The most common causes of blockages

In the kitchen, fat, oil and grease poured down the sink are the single biggest cause of blockages, because they cool and solidify inside the pipe, gradually narrowing it until nothing can pass. In bathrooms, hair combined with soap scum builds up in bath and shower wastes over time, forming a dense plug that slows drainage before stopping it altogether.

Toilets are most commonly blocked by items that were never designed to be flushed, including wet wipes, cotton buds, sanitary products and excess toilet paper. Even wipes labelled as flushable often do not break down the way toilet paper does and are a leading cause of blockages both inside the house and further down the public sewer network.

Traps, grease and hair build-up

The trap beneath a sink or basin is often where a partial blockage first shows itself, since it is a narrower, U-shaped section where debris naturally collects. This is usually the easiest part of the system to access and clear, either by unscrewing the trap itself or using a plunger to dislodge what has built up.

Bath and shower wastes tend to collect hair just below the plughole or slightly further along, and a flexible drain snake or wire designed for this purpose can often pull out a blockage that a plunger alone will not shift.

What not to pour down your drains

Fat, oil and cooking grease should always go into a container and into the bin once cooled, never down the sink, even with hot water running, since it will simply solidify further along the pipe once it cools. Coffee grounds, food scraps and rice can also cause problems if regularly washed down a kitchen sink.

In the bathroom, only the three P's, pee, poo and paper, should go down the toilet. Wet wipes, cotton buds, dental floss, sanitary products and nappies should always go in a bin, regardless of packaging claims about being flushable.

Plunging and rodding explained

A plunger works by creating pressure that pushes and pulls a trapped air and water blockage, and it is most effective on blockages close to the fitting itself, such as a sink or toilet trap. It rarely helps with blockages further down the system because the pressure cannot travel that far through bends and junctions.

Rodding uses flexible rods pushed through an inspection chamber or rodding point to physically break up or dislodge a blockage further along the pipe run, often outside the house where the drain runs underground. This is typically needed when a blockage affects more than one fixture at once, for example if both the kitchen sink and a downstairs toilet are draining slowly, which usually points to a shared section of pipe rather than an isolated fixture issue.

When it becomes a shared or public sewer issue

In the UK, drainage responsibility generally splits at the boundary of the property, or more specifically wherever the pipe becomes a shared drain serving more than one household or joins the public sewer network. Blockages within your own private pipework, from the fixture to that point, are your responsibility, while blockages in a shared or public sewer beyond that point are the responsibility of the water company.

This distinction matters because water companies, such as those covering the Hertfordshire area, generally handle blockages and repairs to public sewers free of charge, whereas private drain blockages and repairs on your own property are chargeable. If several neighbouring properties are affected by the same blockage, it is a strong sign the issue sits in a shared or public section rather than being isolated to one home.

Signs of a collapsed or damaged drain

Recurring blockages in exactly the same spot, gurgling noises from toilets or drains, bad smells around outside drain covers, and damp or sunken patches in the garden above a drain run can all indicate a collapsed or cracked drain pipe rather than a simple obstruction. A CCTV drain survey is usually the most reliable way to confirm this, since it allows a camera to be run through the pipe to identify cracks, root ingress or a collapsed section.

Older Victorian terraces in and around St Albans sometimes still have original clay drainage that has shifted or cracked over the decades, and a survey is often the only way to properly diagnose why blockages keep coming back.

Prevention that actually works

Fitting a simple hair catcher over bath and shower plugholes, disposing of fat and grease in the bin rather than the sink, and being strict about only flushing the three P's will prevent the vast majority of household blockages. A periodic flush of hot water down kitchen sinks after washing up also helps stop grease settling and hardening inside the pipe.

For households with a history of recurring blockages, an annual or biennial drain clearance or CCTV check can catch a developing problem before it becomes a full blockage or an expensive repair.

Frequently asked questions

Can I use chemical drain cleaner on a blocked sink?

It can work on very minor blockages, but repeated use can damage older pipework and is less effective on solid blockages such as grease build-up or hair further down the pipe. Plunging or rodding is often safer and more effective.

Why does my toilet gurgle when I run the kitchen tap?

This usually indicates air is being trapped somewhere in a shared section of pipework, often pointing to a partial blockage further along the drain run that is affecting more than one fixture.

Who is responsible for a blocked drain outside my house?

It depends on where the blockage sits. Private pipework serving only your property is your responsibility, while shared drains or the public sewer network are generally the water company's responsibility.

Are flushable wipes actually safe to flush?

In practice, most do not break down the way toilet paper does and are a common cause of blockages both in household pipework and further down the sewer network, so it is best to bin them instead.

How do I know if I need a CCTV drain survey?

If blockages keep recurring in the same spot, or you notice gurgling, bad smells or damp patches in the garden above a drain run, a CCTV survey is usually the most reliable way to find out what is actually happening underground.