Boston Standard Plumbing & Heating: Toilet Flush Technologies, Part 1

Power outages remind us of how difficult life can be without modern conveniences, but going without one relatively recent addition to modern households can be downright torture! I’m talking about the modern flush toilet. In Boston, there are a variety of toilet technologies in use, from the very old to the most modern. As Boston plumbers, we see it all.

Toilets have been around for a long time. Archaeological evidence from Britain as far back as the 31st century BC shows us that some households at that time had hydraulic toilets. Virtually all homes in the Indus Valley had flush toilets connected to underground sewer systems in the 26th century BC. Flush toilets were also used throughout the Roman Empire until the 5th century AD, when the Roman Empire fell, and flush toilet technology was for the most part, lost in the Western Hemisphere.

In about 1200, an Arabic inventor developed a combined sink basin and flush toilet. The user would use the toilet, wash his hands and then drain the waste water to flush the toilet. (These water-saving toilets are making a comeback in Asia and Europe today.)

But where did the modern toilet come from and how exactly does it work? Today’s toilet is the product of a lot of small innovations on the user’s end, and the creation of modern sewer (or septic) systems. Most of the important inventions involved valves that started and stopped the flow of water; waste containment systems or sewers; and traps that both hold the water in the bowl and prevent noxious sewer gases from escaping into the living space.

In the 1880’s in Britain, Albert Giblin and Thomas Twyford designed different toilet systems, which Thomas Crapper built. Unbelievably, there is no relationship between Thomas Crapper’s name and the word “crap.” “Crap” (whose meaning hasn’t changed a bit) entered the English language long before Thomas Crapper entered the world!

Crapper popularized (but did not invent) the siphon flush system, which we still use heavily today. Additional innovations have allowed the use of pressurized water to empty the bowl more reliably, provide shorter recharge times between flushes and supply a self-cleaning mechanism to keep the bowl in good shape. These pressurized systems are most often used in commercial appliations.

Most residential toilets are of the gravity-fed variety. Basically, these toilets have a tank of water suspended above the bowl. The amount of water in the tank varies, based on the age of the toilet. The newest toilets use anywhere between 1.28 and 1.6 gallons of water per flush. Older toilets may use more than 5 gallons per flush.

Each gallon of water weighs 8 pounds. The toilet tank has a strong flapper valve at the bottom, which prevents water from leaking into the bowl. When the flush handle is depressed, the wide flapper valve at the bottom of the tank opens and the tank water rushes like mad down into the bowl. With older toilets, the more water you have in the tank, the more sustained pressure you can create in the bowl. The newer toilets operate differently, and as you’ll see in my next post, they’re just as effective at clearing the bowl as the older water-hogs are.

A trapway, which is built into the porcelain of the pedestal, is set at a very sharp angle and makes an upside-down U-shaped bend. You can see the trapway built right into the porcelain if you look near the base of the toilet almost directly under the tank. When the water in the bowl reaches the height of the inside curve of the U bend, a siphon is created and the wastewater is sucked out of the toilet and down the soil pipe.

On the topside of the toilet, the water rushes out of the tank and lowers a float valve. When the float valve reaches a certain angle, it opens a fresh water valve to refill the tank with clean water. Meanwhile, the flapper valve at the bottom of the tank closes to hold the fresh water in. As the water level in the tank rises, the float valve rises, too. When the float valve reaches a certain, pre-set level, the fresh water valve closes and the toilet is ready for the next flush.

If the float valve is not adjusted properly, some fresh water may leak into the tank. To prevent overfilling, there’s a relief tube that has a separate drain path around the flapper valve and into the bowl. If your float valve isn’t working properly, you’ll hear regular drainage into the bowl and the water level will rise. Once it fills the trapway, the water will drain out of the bowl.

On the other hand, if your flapper valve is leaking, you’ll still hear draining water, but periodically, your tank will fill for a short period, then shut off. The excess water will also fill the bowl. When it fills the trapway, the bowl will drain.

If you’re having trouble with a leaking toilet, and you don’t have the tools or the time to make a repair, contact the professionals at Boston Standard Plumbing & Heating. We’ll be happy to fix your leak. We can even recommend water-saving toilets that we know you’ll be pleased with. Contact us at (617) – 288-2911 anytime!

In my next post, I’ll talk about new flush technologies and how they can save water without sacrificing performance.