Smelly Drains- Causes and Solutions

What causes sewage and Drain smells?

There is nothing worse than a smell in your kitchen or bathroom that you simply cannot trace or eliminate.  All the disinfectant in the world poured down the sink only relieves the smell temporarily - a sewage smell that seems to stink of the drains.

Causes of Smelly Bathrooms and Kitchens

• The new bath or shower has a continental 'easy-plumb' waste fitted.  These are very common in new bathroom fittings, especially showers, as they enable a low profile shower tray to be fitted.  The problem is that they do not have a trap and sewer gases come back up the pipes if the plug is not permanently in place.

• The septic tank drains have 'backed-up' to the soil vent pipe inlet (if fitted outside the house, as is normal in older houses), blocking it.  This is almost always caused by a failed soakaway and requires immediate remedial work.

• If the sink or bath has not been used for a while, the water in the traps may have evaporated, allowing drain gases to leak back through the plug holes.  If this is a regular problem, fit HepVO self-sealing 'dry' traps.

Images courtesy of Humm-Busters Ltd.

• The soil vent pipe is blocked (birds nest?) too small or absent, causing a 'syphon' effect when water is flushed down the drains and creating a semi vacuum in the pipe  This pulls water out of the trap, causing an imperfect seal and allowing the smell to leak back through the plug hole.

Image courtesy of Humm-Busters Ltd.

• The soil vent pipe (SVP) ends in the loft space.  There are air current in the loft space which is never totally sealed, so the smell leaks out to the outside.   But on still and 'heavy' days the heavy gases, such as Hydrogen Sulphide, may find their way into the living spaces.   If you have an open soil vent pipe in your loft space fit a Maxi-Vent to solve the problem.

Images courtesy of Humm-Busters Ltd.

• The soil vent pipe is too close to a window opening. This means that in certain wind conditions smells will blow in through the open window. You can either fit a Maxi-Vent together with the Aluminium Cover to the external pipe or, if you have loft access, cut a section out of the Soil Vent Stack and fit a Maxi-Vent to the top of the lower section.

• Soil vent pipes which are not covered by a cowl or vent cap.  When the wind blows from a direction that is on the opposite side of your house to your SVP, then air can be forced down the SVP as it drops over the roof.  Trees and other buildings in the vicinity can have the same effect when the wind is in a certain direction.  The gases that should be released by the SVP then are forced back into the drain system - and into your house, increasing your problems. The Maxi-Filtra and Maxi-Vent will stop all problems caused by wind speeds and direction.

But it stinks outside!

• No separate septic tank vent.  If your septic tank is more than 10 metres from the SVP, then the SVP cannot vent it, as it is too far away.  In these cases, the Septic Tank requires its own vent pipe on the outlet side of the tank, which must be situated within 10 metres of it and a minimum of 1.4 metres high.  This should be fitted with a Maxi-Vent to prevent odours escaping from the vent pipe.

• Quite often, particularly on Barn Conversion sites which are designed around a courtyard, the gases from the SVP's drop and become 'trapped' in the yard due to the still conditions there.  Trees, other buildings and the general topography of the area can also interfere with the efficiency of the SVP.  The lack of 'draw' on the SVP also causes gases to escape from manhole covers and septic tank lids.  To address the problem, fit a Maxi-vent to the outlet of the SVP.

• The septic tank vent pipe can also cause smells if it is too low or downwind.  To get rid of the smell fit the Maxi-Filtra. This will allow two-way ventilation but will block the sulphides that cause the stink.

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