Industry Knowledge

Understanding Siphonic and Washdown toilet

Over 4 billion households worldwide have access to proper sanitation in their homes. In spite of that, the majority of home-owners have little knowledge about how their flushing system works and the common misconception is that ‘they all work the same way’ when actually they don’t.

What is Siphonic & Washdown flush

Toilet trapway display

Wash Down: In a wash down action toilet, the water from the tank pours into the bowl and washes the material down the outlet. It is a ‘pushing’ action only, and does not evacuate the bowl. Waste is simply ’pushed’ by free flowing water out of the trapway (usually 4” in diameter). These toilets have small (4”x 5”) water surface areas in the bowls that are deep down in the bowl.

Siphonic : In a siphonic action toilet, the trapway fills with water during the flush which initiates a siphonic action which ‘pulls’ material out of the bowl while the water entering the bowl from the tank through the jet and the rim ‘pushes’ material out. This simultaneous pushing and pulling completely evacuates the bowl during every flush. Normally, the siphonic method employs a smaller outlet (usually 2” diameter).

The Science Behind the Flush

Comparsion picture of siphonc & washdown toilet

There is no surprise that the key element that powers a flush is water, however many people are uninformed about where the water comes from, where the water goes and more importantly how the water is rushed into the toilet bowl without overflowing. There are two main components in a toilet tank; the filling valve refills water into the toilet tank after every flush and the flushing valve releases water from the toilet tank into the toilet bowl. Once water has been released into the toilet bowl, it will carry the waste in a funnel known as the ‘trapway’ leading to the septic tank. The size and shape of the toilet bowl and trapway is the differentiating factor between a siphonic and washdown toilet.

Siphonic Toilets: How they Work?

How siphon toilet works

A siphonic flush system also known as a gravity flush system uses vacuum to pull waste from the toilet bowl into the trapway. This is done by the shape of the trapway acting as a siphon. When the flush lever is pulled, the flush valve releases water into the toilet bowl in two ways; firstly through small holes around the seat rim to clean the bowl and secondly through a hole known as the ‘siphon jet-hole’ which shoots water into the trapway, initiating the siphon effect.

Features of a Siphonic Toilet?

Rimless siphonic one piece toilet        siphonic one piece toilet

  1. S shape trapway (without skirted design)
  2. Small toilet bowl hole as a result of narrow trapway
  3. High water-level in toilet bowl.
  4. Long toilet-bowl base
  5. Siphon-jet hole placed opposite the waste hole
  6. Fully glazed trapway allows for a smooth surface that ensures a strong complete flush

The Benefits of a Siphonic toilet

1.Cleaner toilet bowl surface (seated rim hole cleansing)
2. Flush system produces minimal noise
3. Less likely prone to odor due to high water level

Washdown Toilets: How they Work?

The washdown toilet uses the weight and the gravitational current of the water to push waste from the toilet bowl into the trapway. Due to the fact that a washdown toilet has a short and wide trapway, waste is easily able to enter the trapway with the sheer force of water surging out from the tank.

rimless washdown wall hung toilet

Features of a Washdown Toilet?

1.Usually uses a push-button flush instead of a standard lever flush

2.Skirted design as there is no S-shape trapway to conceal

3.Short/wide trapway

4.Smaller water surface area

5.Large waste hole as a result of wide trapway

6.Most Washdown toilets come with dual flush push button which can be used to be water-efficient

The Benefits of the Washdown Toilets

1.Compact in size due to its short bowl base

2.Can handle heavy loads due to its ‘wide’ trapway

It All Comes Down to Preference!

As flushing systems have evolved over the years, we now have the privilege of evaluating which of these systems best fits our personal needs and wants. At FOHOME, you will be able to find a wide range of Siphonic & Washdown toilets . You may find out more on our siphonic and washdown ranges in the link below: