Low flush toilets come to roost?

[Dougster]

There are already threads here on this topic such as "Low flush toilets causing sewage pipe clogs???"
but here’s an interesting recent (2015) MSc thesis from Kansas State U suggesting further study may be needed:

http://krex.k-state.edu/dspace/bitstream/handle/2097/19223/ReneLe2015.pdf;sequence=1
DRAIN LINE CLOGS WITH A 1.6 GALLON PER FLUSH WATER CLOSET
…
CONCLUSION
…
“The information in Chapter 3 highlight that further research about pipe line clogs should be conducted before enforcing water closets that use less than 1.6 gpf. Manufacturers have ensured that waste will clear the bowl, but there is data to suggest the amount of water from a 1.6 gpf water closet cannot clear 30 feet of four inch PVC DWV piping at 1/4" per foot slope, and that a minimum of four additional flushes are necessary to clear the pipe line.”​

BTW California has a partial exception to the 1.28 gpf maximum:

http://leginfo.legislature.ca.gov/faces/billNavClient.xhtml?bill_id=200920100SB407
…
1101.7. This article shall not apply to any of the following:
(a) Registered historical sites.
(b) Real property for which a licensed plumber certifies that, due to the age or configuration of the property or its plumbing, installation of water-conserving plumbing fixtures is not technically feasible.​

I have an old house with 58 y.o. toilets and 4 inch waste lines.

Have any plumbers here been called on to certify that low flush toilets will not work in an older residential DWV system?

 

[FullySprinklered]

I remember seeing my first 1.6 gal flush toilet with my boss, on display at the supply house. We sort of looked at each other for a moment and I asked him if he thought that 1.6 gallons of water would carry the load to the road, so to speak. He was concerned, to say the least. No way to say that it would work that well unless all the drains out there were perfectly done with the correct slope, etc.

 

[Sponsor]

 

[Gary Swart]

Isn't is strange that with low flow toilets being mandated since the early 90's there must be many thousands now in use all over the country. Now some naysayer comes along and says that you must have more water to carry the waste to the sewer main? Come on guy. Sure the first low flow toilets often had design problems and didn't do a good job of flushing, but this did not cause massive drain line clogging.

 

[Terry]

My mothers home has 250 feet of old sewer line. It works fine.
All of her toilets are 1.6 gallons or less.
A wall hung American Standard Flushmate, 1.6
A wall hung Gerber gravity, 1.28
A floor mount gravity 1.6

New 1.6 gallon toilets tend to have larger 3" flush valves and the water goes out much quicker.

 

[FullySprinklered]

I guess the engineers and designers took everything into account. It was a source of worry early on since everything new in the plumbing industry has had a fairly high rate of failure; Orangeburg pipe, Quest pipe, drum traps, failing PRVs, blown out expansion tanks, and so on. I recycled a five gallon bucket full of prvs yesterday morning.
When I was doing new houses, I would tie in the washer box upstream of as many fixtures as possible. The thinking was that a good shot of hot soapy water might do something good towards keeping the trunk line swept clean. Even if the fall on the pipe isn't quite right.
Had a little old lady customer who had lived in her current house for 28 years. She'd been pouring grease down the kitchen sink for 28 years before I showed up to unclog her sink. She didn't know she had a problem partly because she didn't use much water. After much effort, I took down thirty feet of 3in iron pipe, replaced it with pvc, and rooted another 30-40 feet with a rented snake. It was freaking solid except for a narrow Drano channel cutting through the grease plug from hell.
Point is, the way you use water has a bearing on how well things work.
Heck, I live out in the country. Bodily function doesn't necessarily involve plumbing every time.

 

[CountryBumkin]

Heck, I live out in the country. Bodily function doesn't necessarily involve plumbing every time.

Hillbilly

 

[Jadnashua]

Even an old 5-6 gallon flush toilet may not have carried the waste all the way to the sewer! As long as the line is sloped properly, subsequent uses, which often will include more constant flows like showers, washing machines, etc., will clear the line. If you have a poor joint or a belly, that can make a bad situation worse. The outlet of the toilet is rarely more than a bit over 2" ID, going into at least a 3" pipe, and often getting to a 4" or larger one. There's no way you'll scour the pipe clean with that flow...the pipe must have gravity to eventually do it without obstructions.

 

[FullySprinklered]

Hillbilly

I get a kick out of seeing if I can get my pants up before the blue flies get there.