[Greenbuilding] history of toilet flush volume

[Reuben Deumling]

"Toilet manufacturers in the U.S. gradually began to reduce the water
consumption of toilets in the 1960s. By 1980, the water consumption of most
toilets had dropped from an average of 5–7 gallons per flush (gpf) in the
1950s to 3.5 gpf (from 19–26 to 13 lpf). A push to go well beyond that level
of water use emerged in the 1980s."

I would consider this a fair representation of conventional wisdom on the
subject. It is from the very fine article in EBN titled "All About Toilets"
seehttp://www.buildinggreen.com/auth/article.cfm?fileName=130101a.xml&page=1

Given the historical sizes of toilet tanks, I have some difficulty believing
the 7 gpf figure as an average. 7 gallons is very nearly a cubic foot, and I
should think that would require the portion of the tank below the water line
to be at least that voluminous. I say at least because it is not uncommon
for US toilets to flush in such a manner that the flapper drops back down
before the full volume within the tank has been drained away. Can anyone
confirm the existence of a 7 gpf toilet? or recall toilets made before WWII?

Thanks.

Reuben Deumling