Does toilet trapway size matter?

I'm thinking of buying the Toto Dartmouth which has the G-Max flush. (We're tired of plunging.) My husband thinks the American Standard Champion will work better because it has a 2 3/8 inch trap opening compared to 2 1/8 inches on the Toto. Will the size difference affect the flush? Thanks!

Most trapways are 2-1/8" with the larger (3" or more) flush valves.

That has been a good size.

Some companies are using slightly bigger valves and trapways, mostly so they can say "bigger".

Toto was about 15 years ahead of the others in coming out with the new design that has just recently been copied by others.

Is bigger better, or is it marketing hype?

There isn't that much difference between 2-1/8" and 2-3/8" to make much difference. You're talking 1/4".
If you have waste leaving your body that is bigger than 2" in diameter, then maybe it does.
Most people don't.
The MaP testing is based on 7/8" in diameter waste.

Both toilets use siphon flushing. Too much size, and you loose siphon. Otherwise there wouldn't be a limit on size.

The biggest flushing problem I"ve had with a Champion in a friends home, was when the trip lever starts to wear in and it doesn't let enough water out of the tank to complete a flush. That has nothing to do with size though.
I replaced the tank on that one, and so far it's doing the job. That also fixed the the leaking seal problem.
I don't like how shallow the bowl is though. The deep part doesn't seem placed right.

Champion Reviews

If size does matter to you, and it could with certain medical conditions which results in large than normal bowl movements, you could consider something in the 3" to 4" range, which the Caroma toilet uses. The Caroma uses a Wash down flush.

The Caroma doesn't flush as much miso paste as the others at one time, but with the larger openings, you can drop bigger things through it.

https://terrylove.com/forums/index.php?threads/best-toilet-for-large-bms.60540/

That all being said, most of the new toilets that use a 3" or larger flush valve and a trapway of 2-1/16" or larger will flush better than previous versions.

Area matters

"There isn't that much difference between 2-1/8" and 2-3/8" to make much difference. You're talking 1/4"."

Flow rate is proportional to area for the same head (pressure).

(2.375 squared)/(2.125 squared) = 1.249.

The 2 3/8 unit has 25% more area.

You guys are killin me. The area of a circle equals pi times the radius (1/2 the diameter) squared. there is a 20% difference between the two sizes in question. Regards, Dick

Somebody needs a new calculator.

Area = Pi x Radius squared = Pi x diameter squared /4

Pi = 3.14159

Area of a 2.375 dia circle is 4.43013

Area of a 2.125 dia circle is 3.54656

4.43013 / 3.54656 = 1.249

That's 24.9% more area.

You're right of course. The smaller is 80% of the larger which means the larger is 25% larger than the smaller. The % difference depends on which one you use as the base, and I used the large one which is not what we are trying to determine.

A very old thread, but the lesson is still the same. I have found over time that the TOTO trapway outperforms the Champion trapway, even though there is a small size difference.
I've had customers that started with TOTO, switched over to Champion on their next purchase, and then had me pull them and replace them with TOTO. They had been reading CR, the two guys with the white coats that do their best to stay clean and write reviews. I, on the other hand, do get my fingers dirty. A little dirty, because I have been buying rubber gloves, which helps. I have pulled and installed thousands of toilets in my career, listened to my customers, installed products in my home, my kids home, my friends homes and done way more research than any normal person should have ever done. A little wack, but that's me.
Yes, the Dartmouth has been a very good choice, though this many years later, could be hard to get. The new Drake 2021 toilet have been doing well for my customers. CST776CEG and CST776CEFG

Terry said:

A very old thread, but the lesson is still the same. I have found over time that the TOTO trapway outperforms the Champion trapway, even though there is a small size difference.
I've had customers that started with TOTO, switched over to Champion on their next purchase, and then had me pull them and replace them with TOTO. They had been reading CR, the two guys with the white coats that do their best to stay clean and write reviews. I, on the other hand, do get my fingers dirty. A little dirty, because I have been buying rubber gloves, which helps. I have pulled and installed thousands of toilets in my career, listened to my customers, installed products in my home, my kids home, my friends homes and done way more research than any normal person should have ever done. A little wack, but that's me.
Yes, the Dartmouth has been a very good choice, though this many years later, could be hard to get. The new Drake 2021 toilet have been doing well for my customers. CST776CEG and CST776CEFG

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Your update is timely for me. There is a struggle with our toilet constantly being clogged. Frankly, I am tired of it. Is the Drake your recommendation? I noticed it doesn't have their G Flush "technology" which I thought was the aid to help prevent clogs.

Hawkins said:

Your update is timely for me. There is a struggle with our toilet constantly being clogged. Frankly, I am tired of it. Is the Drake your recommendation? I noticed it doesn't have their G Flush "technology" which I thought was the aid to help prevent clogs.

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G-Max when it first came out was a 3" flapper dropping 1.6 gallons. E-Max was 1.28 gallons. In some places you can still get the 1.6 tanks, though even the 1.28's work fine. TOTO has a sweeping trapway that directs the contents of the bowl downward into the drain. Did I say that right?
Unless there is a medical condition happening, the Drake works very well. I don't know which toilets you're having problems with, but most all of the brands have stepped up their games in the last ten years.
So........which toilet do you have and what year was it installed?

The shape of the trapway plays a big part in how well the toilet flushes. A bigger trapway that tries to make sharp turns often won't perform as well as a slightly smaller one that has smooth curves. If you look at the side of many toilets you can see the trapway path. On a lot of them, it tries to make a nearly right-angle turn into the drain. On a well-designed toilet, the outlet is already pointing the waste down into the drain at the outlet. Good design often trumps bragging rights on size.

Terry said:

G-Max when it first came out was a 3" flapper dropping 1.6 gallons. E-Max was 1.28 gallons. In some places you can still get the 1.6 tanks, though even the 1.28's work fine. TOTO has a sweeping trapway that directs the contents of the bowl downward into the drain. Did I say that right?
Unless there is a medical condition happening, the Drake works very well. I don't know which toilets you're having problems with, but most all of the brands have stepped up their games in the last ten years.
So........which toilet do you have and what year was it installed?

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I believe I have a Mansfield 160? Builder ("Luxury Home Builder") installed in late 2018. I don't believe there's a serious medical condition that exists; however, truly looking for the clog proof toilet. We seemed to have ample problems with this one upon moving in (new construction home) and it's not the TP giving the problems. Some problems I can understand (due to size) but it's just getting to the point that I want to change because of the constant problems.

jadnashua said:

The shape of the trapway plays a big part in how well the toilet flushes. A bigger trapway that tries to make sharp turns often won't perform as well as a slightly smaller one that has smooth curves. If you look at the side of many toilets you can see the trapway path. On a lot of them, it tries to make a nearly right-angle turn into the drain. On a well-designed toilet, the outlet is already pointing the waste down into the drain at the outlet. Good design often trumps bragging rights on size.

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I get what all are saying. I know the Champion 4 boasts about the trapway size but all this is so confusing to someone like me. I want a "clog proof" toilet (within reason of course). The Champion 4 talks about a bucket of golf balls which is impressive, however, I am not a rabbit or deer -- I need something that works for me.

The Mansfield 160 was not a good one. I pull those all the time.

The SHAPE of the trapway is as important and maybe more a factor in how well the toilet flushes. Take a look at this Toto and notice the shape of the trapway, and how when the waste exits the toilet, it is pointing it down into the drain SS-01990_CST786CE(G).pdf (totousa.com). Now, look at this Kohler and notice how the path is flat along the bottom then makes a much sharper right-angle turn to the drain. K-3999 (kohler.com)

Now, you can't view the pathway on all toilets, but if you can, viewing it with this in mind: things don't like to go around right-angle bends! They work much better if you make the bend more rounded and gradual. Human waste in a healthy person is fairly flexible, but not always...sometimes it's long and hard, and that can make it tough to get out along the path. SO, diameter DOES matter, but the shape of the path is as important, if not more.

THe average human waste doesn't have a huge diameter, but the length and firmness can vary unless you have some medical issues and it can be like a log.

So I am only speculating but I suspect what I have is this:
https://www.mansfieldplumbing.com/wp-content/uploads/2015/04/117-160-Alto.pdf (Which is a Mansfield 160...I dont know if it's the alto or not.

But i imagine my problem is that near 180 degree turn at the top of the trapway? Seems pretty tight compared to the two you displayed

I tried to look at the tech specs of the Champion 4, Toto, etc. Just wondering if you all had a recommendation. Without too graphic, it looks like the Champion can support the length and girth (haha) but curious to see what recommendations you all have

Hawkins said:

tried to look at the tech specs of the Champion 4, Toto, etc. Just wondering if you all had a recommendation.

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Terry had a clear recommendation in #7. That is a moderately priced toilet that functions well.

Now if you have other criteria, such as wanting one-piece or skirted for some extra money, say so.

The TOTO has been working better than the Champion for my customers.
I wind up pulling and tossing Champions every so often.

I’ve been looking for a new toilet for weeks, searching the web, trying to decide which would be the best clog-free toilet. I would like a skirted toilet that performs well. I have one TOTO toilet (the Aquia IV) which I’m happy with, but it’s installed in a low-traffic bathroom. Also, I don’t love that it has very little water in the bowl, which results in a dirty bowl after #2. Is there a toilet that you recommend, which is (mostly) clog-free, skirted, that has a high water level? Thank you!

I've always been an American Standard groupie, the debate about trap diameter above illustrates that the 2-1/8" trap is better for velocity, but also yields a better siphon (suction). Their new toilets also have "Vormax" bowls, instead of a rim with small holes it uses a single injector that forces the water to flush in a swirling vortex to clean the bowl.

* Just had a chuckle at the old debate from 2006 involving Bob NH above, where someone presumes volume increase is equally proportional to linear diametric measurement.

Plumbers learn this in school in both drain sizing and vent connections.... a linear increase across diameter is an exponential increase in volume.

Natslie said:

TOTO toilet (the Aquia IV)

Natslie said:

it has very little water in the bowl

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Its a problem for all (that I know of) dual flush toilets. In order to satisfy the lower flush requirement, they have a smaller water spot.