My grandmother had that saying in her old house in the Appalachians of Northern Georgia. Her septic tank wasn't up to the task when there was a full house. I was about 10 or 12 years old at the time, and I did something in the john that can only be described as horrendous. Well, grandma went in a little while after me, came back out and said in that sweet Georgian drawl of hers, something to the effect of "honey, I know my tank don't do so well, but when you do something like THAT, flush it down please."
I turned red as a fire truck, the whole family laughed heartily for a good spell!
2014 Jay Flight 28 BHBE
2015 RAM 2500 6.4L HEMI, Tradesman 4x4, 3.73
Blue Ox SwayPro (BXW 1503)
Upgraded from an REI internal frame backpack and a Eureka 1/2 dome tent!