Clearing Blocked Drains and Gullies

When domestic waste systems go wrong, speedy correction is most important. The entire system, from taps to flushing and storage cistern mechanisms, should be inspected from time to time to keep them trouble free. Below ground, manholes and pipe-work should also be inspected periodically. Traps and gullies are the remaining areas of possible trouble.

Waste systems do not generally require a great deal of attention but it is important to ensure that, during the winter, any external services are free of residual water – such as may happen in runs of horizontal pipe-work or if a waste pipe should sag.

One way of helping to prevent large blockages is the routine inspection and clearing of waste traps, gullies and manholes. A blocked waste trap can usually be cleared with a rubber plunger cup.

When using this, half fill the sink or basin with water. Block, temporarily, any overflows and then work the plunger up and down over the drain exit, with a vigorous, jabbing motion.

Waste traps

If the blockage persists, this will necessitate access to the trap which provides the water seal. This entails removing a plug in the side or bottom of the trap. First, place a container of sufficient size beneath to collect debris and water when the plug is unscrewed.

Traps may be made of copper, lead or plastic. Do not impose excess strain on the trap or you may fracture it. Support it while you are undoing the plug and then hook out any debris with a piece of wire.

WC pans

A blocked WC pan may respond to treat- ment with a plunger but this should be used with great care to avoid stress on the pan which may cause it to break. It is, however, unusual for blockages to occur or persist in the soil system.


Blockages may occur in manhole inspection chambers at point of entry or outflow for a variety of reasons. The main causes are roughened surfaces or fractures, permitting debris to adhere, or benching which is inadequate-perhaps too low, allowing an obstruction to build up.

Fractures or other damage should be speedily rectified, since these would represent a public-health infringement and health danger. Flaws in benching should also be corrected; the benching should be smooth, and gently sloped on either side of the outflow pipe.

Drain rods

Sometimes, a blockage may occur through no fault of the system. Normally, this can be cleared easily by prodding free with a stick. In other cases, you may need a set of drainage rods, together with fittings, to deal with a variety of circumstances.

Rods screw together and are each about lm long. These provide reasonable flexibility, allowing them to be fed along a blocked pipe from within the manhole or along the pipe from outside, in the case of shallow manholes.

The main attachments, which screw on to the head, are a rubber plunger, corkscrew head, hook, scraper and brush head. The brush set resembles those used by chimney sweeps. The corkscrew is intended for lifting plugs in manholes but can also be used to clear blockages. Rods can be bought or hired.

To find a blockage, start at the house and open up each inspection chamber in turn. When you locate an empty one, this indicates that the blockage is between this and the previous one.

Place a temporary barrier over the mouth of the outflow in the empty chamber. A piece of chicken wire rolled into a ball is suitable and allows water to pass but stops solid matter. Take care, however, that the wire does not enter the pipe and further block it.

Next, attach the rubber plunger and insert this at the blocked-up chamber. Turn the rods in a clockwise direction as you insert them as this ensures that they do not unscrew. You should, in most cases, be able to push the obstruction clear. If this fails, you will have to try the hook. Use the scraper to remove debris adhering to surfaces.

Once the blockage is dislodged, remove it, or break it down, and finally flush with water to disperse. Then use a hose to flush out the length of drain. Use the brush to clean off any encaked debris as this may cause a blockage to recur, then sprinkle disinfectant.

Once the blockage is cleared, check the cause as a flaw or deterioration may need to be remedied. Inspect carefully before replacing the inspection cover on the manhole.

Testing Manhole Covers and Types of Manhole Covers

Where a manhole cover is broken and needs replacing it is generally necessary to buy a new rim as well as the lid, since these are made as a matched pair to ensure a good fit.

Although a matched rim and lid should fit together tightly, they will not provide a totally airtight seal. It is necessary to apply manhole grease liberally to the rim before putting on the lid.

Where the lid is removed for inspection, it is advisable to remove all old grease and repack the seal, which also prevents dirt and foreign matter from getting into the manhole and, possibly, causing a blockage.

Rims are usually set in concrete surrounds, so are relatively simply to replace. To take out an old rim, chip away the surrounding concrete, using a club hammer and small cold chisel. Any deterioration in mortar and brickwork should also be made good.

Care should be taken not to damage brickwork below the rim. Bed this rim or cover frame in a 1:3 mix over the entire area to ensure an even bearing for the frame.

Place the lid in position to avoid twisting the frame; make sure that the cover is evenly in place and will not rock. Check that alignment is accurate with a spirit level.

Benching should be shaped so that it slopes from the channel in the centre to the sides of the manhole at a gradient of about 25mm: 152mm.

It should be made of a mixture of 1:4 (sharp sand) and finished with a steel trowel. It must be kept clean, and if any cracks appear, these should be at once repaired.

When remaking benching, take care not to allow mortar to fall into the gulley-if any does, remove before putting the drain back into commission.

When repairing cracks, a PVA adhesive should be used to bond new mortar. The existing surface should first be cleaned thoroughly with a wire brush.

Brickwork should also be inspected at fairly regular intervals, and if any rendering or faulty pointing is noted, this should be repaired.

Testing manholes

If a manhole defect leads to a loss of water, the fault should be traced, rectified and the manhole loaded and tested continually for an hour, during which there should be no significant water loss.

A fall of more than 25mm in this time would be excessive and not accounted for by absorption within the chamber walls or by dissipation.

The section of drain adjacent to the suspect manhole should first be isolated and charged with water. This is done by means of drain plugs, which have rubber walls, expanded by means of a screw on the centre of the plug body, to fit into the entry point of the channel.

By unscrewing a centre nut, the section can be drained slowly. Always reduce the pressure of water by first releasing this nut, as the pressure of water might drag the plug into the pipe and be difficult to extricate.

Types of manhole

If you have to carry out a substantial repair of an inspection chamber, it might be as well to consider replacement with one of the newer prefabricated units-plastic, concrete or pitch-fibre.

Channels in the base of a manhole can be pre-cast, half-round self-glazed or of pitch-fibre pipe, or formed in a concrete base with a smooth object, such as a tin. These must consist of a 1:4 (sharp sand) composition.

Sharp angles should be avoided in channels as this could lead to blockages.

Manhole sides must be constructed of dense and non-porous bricks, such as engineering bricks, which are able to withstand constant conditions of damp. These should be laid using an English bond.

Where conventional bricks are used, these should be ‘parged’ or rendered to provide the same protection as engineering bricks. Not all local authorities will permit the use of ordinary bricks.

10. November 2011 by admin
Categories: Featured, Handyman Tips | Tags: , , , , , , , , , | Comments Off on Clearing Blocked Drains and Gullies


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