Industry Knowledge

Understanding S-Trap and P-Trap Toilet

Many people invest in properties in hopes to rent them or selling them at a higher price. Oftentimes the home is empty for months or years. That being said, they try to make sure that there is no foul smell from the toilet bowl. That is why most buyers are asked to ensure that a P-trap toilet bowl is installed since it is likely to stop gasses coming from the sewerage system for a longer period of time.

Older homes usually have S-trap toilet bowls and are more likely to have a foul smell if not used for a long time compared to P-trap toilet bowls. Here are some important facts about P-trap and S-trap toilet bowls for homeowners to know the pros and cons of each toilet trap and help them decide which trap type to use.

In toilets, the P-trap and S-trap refer to the shape and orientation of the trap that connects the toilet bowl to the waste pipe.

S-Trap Toilet Bowl

S-trap toilet bowl

An S-trap toilet has a trap that is shaped like an “S”. This type of trap commonly used in plumbing systems. S-trap toilets have a straight pipe that connects the toilet bowl to the waste pipe, and the trap is formed by a bend in the pipe just below the toilet bowl. While S-trap toilets can be easier to install in certain situations where the waste pipe is located in a different position than where the toilet will be placed. The bend in the trap allows for more flexibility in positioning the toilet, which can be useful in older buildings or in situations where the plumbing system is not easily adaptable.

There are things to note before a toilet bowl replacement – one is knowing what your current toilet bowl trap is and where it is located.

A Very Common Trap

Wahdown S-trap two piece toilet bowl

The S-trap toilet bowl is the most common trap used in toilets since it has been used for toilets for more than a century. That is why most older buildings have this type of trap installed and are very familiar to plumbers. An S-trap toilet such as F6106S-1 two piece toilet bowl should be used regularly to prevent the trap from going dry. S-traps are also found in sinks and drains.

Some Present Drawbacks

One of the main cons of the S-trap toilet bowl is that the water in it is likely to evaporate if not used for a long time, especially during dry and hot weather. In addition to the foul smell, vermins such as rats and cockroaches from the sewerage system can come up from toilets through the dry strap.

P-Trap Toilet Bowl

P-trap two piece toilet

A P-trap toilet has a trap that is shaped like a “P”. It is a curved pipe that is designed to hold water and create a barrier between the toilet bowl and the waste pipe. The water in the P-trap prevents sewer gases from entering the room, as the gases are unable to flow back up through the trap. P-trap toilets are more common in modern construction and renovations, as they are more effective in preventing odors and are easier to maintain.

Most new buildings use a P-trap since this design is more effective in forming a water seal and does not dry when not used for a long time. However, when opting for a toilet bowl replacement, it is still essential to check what type of trap you have and avoid mistakes when getting a new toilet bowl.

Traps Debris and Stops Clogging

Some debris may be trapped in a P-trap toilet bowl, especially if it is a heavy object dropped accidentally. However, most wastes are low density enough to be washed away by the water so there is no clogging.

Dry P-Trap

Even if a P-trap is designed to retain water for a longer time, it can dry up if the temperature is high and humidity levels are low, which causes water to evaporate faster. Furthermore, if something highly absorbent is dropped in the toilet, the P-trap toilet bowl may dry up, resulting in foul smells.

Comparsion picture of S-trap & P-trap toilet


Knowing the difference between an S-trap and P-trap Toilet Bowl is essential whenever you are planning for an installation or replacement to avoid making mistakes when getting a new toilet bowl.

S-trap toilet bowls are very common and are usually installed in areas where the drainage is connected to the ground; they have been used for toilets for centuries but are prone to drying up, causing foul smells and vermins like rats and cockroaches to crawl up from it.

The P-trap however is a newer innovation that minimizes foul smells from the sewerage system because it is less likely to dry up, and is used in newer buildings. It is also less likely to be clogged unless something heavy is dropped in the toilet causing it to be trapped inside.

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