| There are several things that would cause this problem. (1) A crack in the bowl that can't be seen,**or** (2) Sometimes a bubble will occur in the casting that causes a hole that allows water to leak back down into the closet bend and out into the sewer. Instead of junking the bowl the manufacture will float a porcelain patch over the hole. Sometimes this patch comes loose and the bowl loses water. A blocked vent could cause a lowering of the water level but this almost never happens. You would hear a gurgle in fixtures with lesser traps first. My bet's on a defective bowl.
Brad posts, " It sounds to me like a defective toilet. I read elsewhere that someone removed the toilet and set it up on sawhorses and filled the bowl full of water to see if it was leaking out somewhere underneath."
I was the plumber that put a Briggs bowl up on sawhorses to check for a hidden leak. It was and Briggs replaced the bowl.
My advice? Replace the bowl. Good luck, Tom |