Low flow toilets: If you raised the tank by two feet.

Wouldn’t that help eliminate a lot of the clogs normally associated with low flow toilets?

(My theory being that the water in the tank would enter the bowl at a higher rate of velocity.)

Modern low-water-usage toilets flush as well (or better) than the old kind.

I have to agree with you here. But, If someone has one of the old low-flow toilets. Well, they sucked. And not in a good way.

Siphoning is a much more important factor in a toilets ability to flush. Raising the tank higher would have minimal effect on the siphon. Current generation of toilets are well designed taking into account the amount of water available per flush.

The original low flow toilets simply took a standard high flow toilet and put a smaller tank on them. This resulted in a generation of poorly designed toilets whose ability to siphon was dependent on more water than the tanks provided. They were terrible. That generation is what everyone has stuck in their heads when they believe low flow toilets are bad. The new ones work just fine and don’t need new concepts like raising the tank applied.

Agreed. Raising the tank would have little or no effect.

So what is the difference in the physics of old-fashioned low flow toilets and the newer ones?

Much larger flush valves, for one.

Yeah, maybe. Except for that shit smear on the bowl because there’s very little water in it.

Yeah, I just replaced my old low flow toilet that was continually getting clogged with a modern one and was astounded at the difference. The old one had a smaller flush valve and the way it would flush was in the familiar flush swirl. So if you’re flushing, you know how the bowl fills up, swirls, swirls, then (hopefully) all goes down the drain with a gurgle? I think the whole process would take about five to seven seconds from flush to evacuation of contents. The new one I have, the water just drops straight down without a swirl and is through the pipes in about a second. Haven’t had a single clog on it yet.

Old-fill the bowl to start a syphon. Bowl fill with water through holes around top ring and a 1/2" hole in bottom of the exit throat. As bowl empties pulls everything with the water.

New- 1" hole in bottom of exit throat. When handle is pushed down Tank empties in just a second or less. All the water goes through the 1’ hole. Velocity carries the small amount of water and solids in the bowl out the back of the bowl and down the drain. Flapper closes and as tank refills some water is diverted to refill bowl.

Maybe it varies by brand. I got a new toilet last year and it clogs. I wouldn’t say it was frequent, but considering that the old ones NEVER clog…

A lot of cheap toilets, low flow or even those from the pre-low-flow era, have small passages through the S-bend. Anything larger in diameter than a golf ball barely fits.

Better toilets have much larger throats. They can almost pass a softball.

You can see how one would clog much more readily than the other.

The “syphon” bowls were an American thing. And I’m not sure how “old” they were - I don’t actually remember them from the 50’s, but I was young then. Our old Aus toilet (on an English model) had a cistern at about 6’. And it did push down and through. They were replaced with a lower cistern that relied on higher volume. And then we got low-flow-that-doesn’t-work-very-well.

I remember seeing, back in the old days, the tank was close to the ceiling. And you pulled a chain to send the water down.

I replaced the one in our house soon after we moved in. Like many of its breed, there was a trick to get it to work. As I recall, one had to pull fairly gently (to prime it?) and then a vigorous but smooth pull all the way and hold.

My father had one years ago. Most of the year you had to put a towel over your head and back when sitting on the commode or risk having water drip on you from the tank.

When my brother bought his current home in Michigan he was unhappy with his toilets. He couldn’t purchase what he wanted legally in Michigan, so he rented a truck and drove to Canada, where he purchased five Michigan-illegal toilets. He then hired a plumber to install them on the sly, paying him in cash.

if you want to see an example of this , watch the Godfather movie. that’s the first time I saw one of those

I noticed this with our dual flush toilets, which have the advantage of a #2 flush of 1.8 g instead of the 1.2 g / flush. They didn’t stay clean. However I moved the water level slightly higher then the ‘max’ level and that made a big difference in the bowl being clean. Not as good as the swirl action of days go by but does take care of most of it.

I have an old high-flow from the 1980s that clogs constantly, there’s the anecdote to cancel out yours.

Anyway, as most have already explained, diverting most of the water away from the rim to the “jet assist” at the bottom of the bowl is one of the big factors, along with the increase in the size of the flapper, allowing the water from the tank to be dumped very quickly. Another thing that was done was to fully glaze the trapway after the bowl. In older toilets it would be just bare porcelain with a rough sandy texture beyond where you could see it. By glazing it that makes everything slide along better. Raising the tank or increasing the water pressure wouldn’t have much impact on this.

These are all still technically siphon toilets. I don’t think that’s ever changed. Washdown toilets, which are popular in Australia and parts of Europe, don’t have the jet assist and pour all their water out of the rim. They do it faster so it basically forces the contents of the bowl out the bottom. It seems to use more water, but that could be just because you see it all. I don’t know that it’s really more effective either, just maybe better in some ways and worse in others.