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Spending a penny and the lowly trap seal

By Fiona Ingham

In 1851, London’s Great Exhibition displayed Britain’s manufacturing and commercial skills of the time. It also housed a true innovation: public flushing toilets. They created excitement among the throngs who were intrigued by the sound and swirling water. They cost a penny to visit, but 800 000 people didn’t mind the cost and paid the toilets a visit. And so the expression “spending a penny” was born. Some sources say that male visitors received a shoeshine as well!

Since then, the water-seal trap in toilets has been perfected. Almost every plumbing system relies on waste traps to prevent odours and bacteria from entering through the drains. The trap is a device that keeps an amount of liquid every time the fixture is used, and the amount of retained liquid is the trap seal. This trap seal also prevents rodents or insects from entering the environment, however unlikely that might be.

These concealed bends are the unsung heroes of a building’s plumbing system, which is entirely concealed and unsung anyway. It is taken for granted, at least by the user, but it’s vital that every waste trap is built sturdily and to a high standard. Allfixtures, including sinks, baths, showers, toilets and urinals, are equipped with a trap.


“There are two basic kinds of traps,” says Willie Knoetze, technical sales representative at Marley Pipe Systems. “A re-sealable trap is better for vertical stacks in multi-storey buildings and is preferred by these plumbing contractors. If there is a big drop in the water level they provide increased resistance to siphonage.”

“A P-trap has a horizontal outlet and an S-trap has a vertical outlet dropping to the floor, but they have exactly the same purpose. A combination of S and P traps are used in multi-storey buildings,” says Knoetze.

“We also have a universal trap, so called because it is a ‘one size fits all’. It’s a very good seller with the home plumber who often doesn’t know the diameter of the inlet and outlet pipes and can be used on most pipe sizes. The home plumber can cut this pipe to size,” Knoetze says. All Marley traps are manufactured locally.

“With single and double sinks, you have a combination trap where the two combine into one,” adds Louis Kruger, technical support specialist at Marley.

The traps come in white PVC or in black rubber and their quality is the same. They perform the same purpose, and so it comes down to personal preference. White is usually preferred when the trap is visible. With the rubber traps, squeezing the “u” section creates a pumping effect that effectively removes the source of the blockage.

“The biggest mistakes made by installers are that they do not push the trap properly over the waste fitting and then it jumps off. Or, they overtighten the clamp and break it. Or they just don’t fit the clamps at all!” says Kruger. “The trap needs to have a minimum depth of 75mm for a water seal.”

These fixtures have a 50-year life span, in line with the usual engineering specifications.


“Householders and commercial kitchens are not meant to put grease down the drain and should be installing grease traps,” says Kruger. He acknowledges that this kind of infringement is not enforced domestically. But commercial offenders, with their large volumes, tend to go the more formal route. Restaurants and formal establishments also face municipal effluence charges for infringements.

When a grease trap is full, it should be placed in the rubbish to go to the landfill, but commercial operations, such as restaurants and malls, should employ maintenance contractors/waste removal companies to collect the grease for reuse. Grease and cooking oil can be recycled to be used as biodiesel fuel for motor vehicles. Several plumbing businesses provide grease trap cleaning services to restaurants, malls, factories, shopping centres and corporate buildings with large staff canteens.

Naturally, all grease traps have to be maintained to continue efficient operation. The frequency of grease and solids removal depends on the food series type and the quantity of grease in the water. The grease and water are separated, with the grease left behind. Good quality grease traps have a high percentage of solids captured and an airtight seal to contain offensive odours and overflow. They can also withstand temperatures of up to 140°C. The outlet baffle prevents grease from entering the waste stream.






P and S traps, mini trap, deep seal, plain or reseal


40mm or 50mm


P and S traps, mini trap, deep seal, plain or reseal



*40mm in certain regions


Bath trap, plain or reseal



*40mm in certain regions

Source: Marley Pipe Systems

A 50mm x 5Omm bath trap.

A combination vertical and horizontal waste trap.



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