.......My uncle (now deceased) related how, as a boy on one of our farms (circa 195_ ?),Grandpa & he were trying to fix a wet spot by digging up an old clay tile to run the cleaner through (they thought it was full of dirt).

What they found was, the old timers came up to a large rock, put the clay up to the rock, and proceeded on the other side on grade & in line. No roundabouts here!

Maybe it was a porous rock!