What does "turtle urine ooze" mean? Is it an idiom? Where does it originate?

"Turtle urine oozes", I heard this in Guo Degang's traditional stand-up comedy "Bee Sparrow". This cross talk is about some deceptions in the past. It said that the old Taoist asked the good man for money, but the good man refused to give it. The old Taoist sat at the door of the good man for three days. When he saw that the good man was indifferent, he left. Before leaving, he wrote the four words "You are an evil person" on the wall of the good man's courtyard. The good man asked someone to scrape off four characters. As a result, one layer was scraped off, but there were still characters on the inner layer. This was repeated no matter how many times he scraped it off, but there were still characters. Everyone thinks that the old Taoist is really capable, but only good people know that this is a trick. It turns out that the good man has been in the profession of Lao Tao before, and he knows what "turtle urine oozes" is about. That is to say, the urine of turtles has the characteristic of drilling inward and constantly seeping in, and the ink used by Lao Tao is added to Turtle urine.

It’s not clear whether this phenomenon is true or not. If it is true, we can only speculate that the turtle's urine contains strong acidic substances that can undergo violent chemical reactions with carbonates or oxidizing substances in the stone, so it can penetrate deep into the stone.