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How to clear blocked drains


1st Jan 2015 Home & Garden

How to clear blocked drains

Calling a plumber can be expensive these days, so here's a handy guide to help you unblock drains 

Before you start

Remember that pipes below ground are laid in straight lines for as much of their route as possible. Where a change of direction is needed, the bend should be less than a right angle and there should be an inspection chamber there. There may be a manhole cover above it, or, in older properties, there may be an interceptor chamber near the boundary before the house drain joins the main sewer.

The first sign of a blocked drain may be the failure of WCs and baths to drain quickly and efficiently, or an overflowing inspection chamber or gully. A gully may be cleared by cleaning. Otherwise, you will have to clear the drain with rods. You can hire rods and various heads. Wear rubber gloves for the work.


  • Drain rods fitted with a 100mm diameter rubber plunger 
  • Pair of long rubber gloves 
  • Strong garden spade 
  • Hose 
  • Disinfectant
  • Watering can

1. Locate the blockage 

You will have to lift the manhole covers; a strong garden spade will raise the edge enough for you to grasp the cover. Inspect the chamber that is nearer to the main drain, septic tank or cesspool than the overflowing chamber or gully.

If it is empty, the blockage is in the drain between this chamber and the higher one or the gully. If the chamber is full, inspect the chamber next nearest to the main drain or septic tank. If the chamber nearest the main drain is full, the blockage is between it and the main drain. If the drain leads to a septic tank and the last chamber is full, have the tank emptied.

2. Clearing the blockage

To clear the blockage in a main drain system, insert the rod fitted with the plunger into a chamber at one end of the blocked section; it does not matter which of the two. If it is the empty chamber, you can see where the mouth of the pipe is, but if you work from the full chamber, you will have to probe with the plunger until you find the mouth.

3. Adding more rods 

Add more rods as necessary to work the plunger along the pipe to the blockage. Always turn the rods clockwise as you work; if you turn them counter-clockwise, they may unscrew and be left in the drain to cause a greater problem. Keep pushing against the obstruction and then withdraw the plunger a little way. If this will not shift the blockage, withdraw the rods and exchange the plunger for a corkscrew attachment, which will break up a tightly packed obstruction.

4. Wet jet

Complete the clearance by directing a strong jet of water down the drain from a hosepipe, or by filling the bath and sink and releasing the water in one gush.

5. Clearing up

Hose down the rods and gloves thoroughly and drench them with diluted disinfectant poured from a watering can.

Interceptor chambers

How to clear blocked drains - Prepared drainage system from plastic pipesCredit: Roman Mykhalchuk

If you have to clear a blockage between an interceptor chamber on your property and the main drain, you will have to insert the rods through the rodding eye. At this chamber, the drain drops through a U-trap similar to the one in a gully.

The trap is there to prevent waste from the main drain from entering your house drains, but it also prevents you from pushing rods through. Above the mouth of the trap, there is a short projection of pipe with a plug in it. When you locate and pull out the plug, you can insert the drain rods through the hole, or rodding eye.

The trap, however, may still be blocked, and you will have to scoop out the blockage with an old garden trowel bent to a right angle. When the chamber and trap are clear, hose them down thoroughly to make sure waste can flow out easily.

You can either replace the plug or you can mortar a piece of tile over the eye. If you need to open the rodding eye again, the tile will knock off easily with a crowbar and hammer.


Testing drains

How to clear blocked drains - A professional drain cleaning engineer inspects a blocked household drainCredit: PaulMaguire

If the drains are not blocked, but a persistent foul smell or unexpectedly wet ground makes you suspect that there is a leak somewhere, arrange for the local environmental health department to test the drains.

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