How To Fix a Leaking PVC P-Trap or Drain Pipe Under Your Kitchen Sink, Wash-Hand Basin or Bathtub

How To Fix a Leaking PVC P-Trap or Drain Pipe Under Your Kitchen Sink, Wash-Hand Basin or Bathtub

How To Fix a PVC Drain Pipe Leaking at Joint.

14 Reasons Why Your P-Trap or Drain Pipe is Leaking

What is a P-Trap?

A P-Trap is a type of waste water trap used and fitted under kitchen sinks, laundry sinks and wash-hand basins. This trap is also often seen behind a toilet (WC) using a much larger 100mm diameter waste pipe, and it can be installed under bathtubs and showers.

The P-Trap derives its name from its shape featuring a horizontal tubular end and U-shaped tube to form a P. Otherwise, there are other types of waste water traps in use today, for example the bottle trap and S-trap.

PVC P-Trap Cross Section Details_2

PVC P-Trap Cross Section Details_2

Who Invented the Plumbing P-Trap?

The P-Trap is also known as the Thomas Crapper trap after its inventor and designer. In 1880, Thomas Crapper redesigned the S-Bend into a much better U-Bend which would later on be called a P-Trap in this modern era. The S-Bend was invented by Alexander Cummings in 1775 as a solution for a foul-proof anti-smell flush toilet drain. The household toilet invented by Sir John Harrington in 1596 was the first mechanically operated flush toilet making use of a gravity water tank, valve and bowl, rather than relying on a diverted manmade stream to flush away the waste. Despite its usefulness, the Harrington flush toilet had one problem – the foul smell from the waste pipe would find its way into the room and entire house. Alexander Cummings came up with the S-Trap, an idea that would prevent foul air from escaping the drain pipe into the house by creating an air-tight water seal in the U-bend section of the trap.

PVC S-Trap Cross Section Details_2

PVC S-Trap Cross Section Details_2

How Does a P-Trap Work? And Why You Have Foul Air from the Sewer in the House

A P-Trap works in a simple way. The U-section of the P-Trap is what makes it useful. It traps water when the tape water stops running or when the sink is completely drained. The trapped water provides an airtight liquid seal that stops sewer gases from passing through to the sink and into the building. Sewer gases have an obnoxious smell, but they can also pose a health hazard due to their toxic elements as well as a fire hazard when ignited.  Sewer gas contains highly flammable compounds like methane and hydrogen sulphide. That’s the reason why you need a P-Trap to shut out these potentially dangerous gases. But a P-Trap only works if there is stagnant water in the U-Bend. Without this water seal, sewer gases will pass through. Conditions which lead to the P-Trap drying up include not using or running water in your sinks for a long time, for example when you go for a months-long vacation. However, it’s not just a dry P-Trap which causes sewer gases to flow into your house. Even if there is a water seal inside the trap, a change in the air pressure on both sides of the drain pipe may cause sewer gases to pass through. When venting (ventilation pipes or stacks) is not installed on your waste water outlets, air pressure will build up in the sewer pipes, forcing the foul air through the water-filled traps and into the building. In this case, aeration will cause bubbles and gurgling which can be heard in the trap.

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