Earlier this year, I did the dye test on the toilet in out small guest bathroom. I found evidence that there was a slow leak - dye color from the tank leaked slowly seeped into the bowl. When the plumber was here for another project, we tried to see if he could seal it, but it was leak that you couldn't see. Small leaks can potentially yield gallons and gallons of wasted water according to Sustainable Works. After much research on other ways to fix, we eventually decided that the only way was to replace it.