Choosing the Right P-Trap Kitchen sink P-Traps come in 1-1/2” standard size, while bathroom sinks use P-Traps of 1-1/4” standard size. The traps also come in different material types such as propylene, ABS, brass (chrome-plated or natural), and PVC.
Plastic traps come in inside-diameter sizes of 1-1/4-in. for a standard bathroom sink; 1-1/2-in. for a laundry sink, bathtub or standard kitchen sink; and two inches for a shower or floor drain.
For instance, bathroom sink P-traps are typically 1 ¼ inches in diameter, while those for kitchen sinks are typically 1 ½ inches. P-traps work by utilizing a water seal in their curve to block sewer gases from entering your home while simultaneously allowing wastewater to pass.
Wash hand basin (bathroom sink) wastes use a 32mm / 1-1/4 inch trap. Kitchen sinks, baths and shower wastes use a 40mm / 1-1/2 inch trap.
What are the sizes of P-traps? P-traps come in various sizes such as 125x110 mm, 110x110 mm, 75 mm, 4x4, 4x4-1/2 inches, etc.
Drain Trap Materials
Several sizes (pipe diameters) are available, including 1 1/4-inch, 1 1/2-inch, and 2-inch. Bathroom sinks usually use 1 1/2"-inch traps, while kitchen sinks usually use 2"-inch traps. Washers are provided that allow you to connect to the 1 1/4" tailpiece from a sink.
P-traps, named after their shape, contain a u-shaped bend that filters wastewater as it enters a plumbing system. The trap is connected to a sink, bathtub, and shower with a J-bend on one end and exits into your drainage system.
Location of the P-trap
The International Residential Code, under the International Code Council, says that the P-trap must hang at a maximum height of 24 inches below the drain. Of course, this measurement depends on the sink's base height from the floor.
P-trap set-out measurement
For a p-trap toilet, the measurement is taken from the floor to the centre of the waste pipe. Most p-trap close coupled suites require a set-out measurement of 185mm.
The vertical distance from the fixture outlet to the trap weir shall not exceed 24 inches (610 mm), and the horizontal distance shall not exceed 30 inches (610 mm) measured from the centerline of the fixture outlet to the centerline of the inlet of the trap.
Most drain openings are 1 1/4 inches, although 1 1/2 inches and 1 5/8 inches are also common sizes.
The water that sits in a trap is what prevents sewer gases from entering a building. The photo below shows a “P-trap”, which is the type of trap you'll find below most sinks, showers, and bathtubs. Toilets have their own built-in traps, and so do floor drains.
Toilet drain pipes are usually 3 inches in diameter. Washing machines and laundry sinks generally need 2-inch drain pipes. Shower and bathtub drain pipes are usually 2 inches in diameter. Sinks usually require a 1.5-inch drain pipe.
Traps shall be not less than 1 1/4 inches in diameter. A trap shall not be larger than the waste pipe to which it is connected.
It is perfectly fine to have (2) “P” traps , one on eash sink of a (2) sink setup. As long as the “P” traps are not Double Trapped ( more than one trap serving a fixture ) then it is fine as long as the weir is sized correctly.
Double-trapping the same sink, like in the two examples below, is also not allowed—although we once listened to a passionate argument by a homeowner that it's actually twice as good. Oh well. It creates an excessively large trap volume and makes the drain more likely to clog.
The bottom pipes used in S-traps are S-shaped, whereas P traps utilise P-shaped pipes so that when water is flushed through these pipes, little water is reserved. While the wastewater is reserved in the S trap, it is only done temporarily in the P trap.
The usual size for a shower drain trap is 2 inches, which is the diameter of the trap. This size is the minimum size that is allowed, which means that you cannot install a trap with a smaller diameter, or the trap is not within code.
How does P-trap Works? A P-trap got its name because it joins two 90 degree joints with a horizontal overspill pipe and allows the whole unit the shape of the letter “P.” One of the joints (90 degrees) is fixed to the exits of the drain of the sink and then connects to another, which contains a water sealant system.
There are three common drain sizes for bathroom sinks, 1.25", 1.5" and 1 5/8 (1.625"). You need to select a drain that is the same size or SMALLER than the hole in your sink. For example, if you have a sink with a drain hole of 1.75", than any of the drains 1.25", 1.5", or 1.65" will work.
Trapways can be no smaller than 1.5 inches in diameter according to the Institute's guidelines. Most toilets have larger trapways than the minimum standard for better performance. The most common sizes for toilet trapways are between 1.75 and 2 inches, although some models can be as large as 3 inches in diameter.