OK a little thread drift here......
A few decades ago I rehabbed a 100 year old house in Cleveland. Tore the entire cast iron soil stack out (basement to third floor roof) and replaced it with PVC. Building department wanted a leak check. This is accomplished by inserting an inflatable ball through the 4" clean out in the basement and inflating it. Then fill the system from the top with various smaller balls at outlets on the way up. No leaky, you get a sign of and the dude leaves.
So, this all done I go down to the basement and without thinking this through completely stick my hand in the clean out and pushed the air valve to release the pressure. The ball deflated and dislodged. It has a chain attached to it with a ring on the other end larger than the 4" of the clean out so it can't get away and block the system somewhere on the way to the street.
So, it runs out of chain, but is now blocking the part of the pipe below the clean out.......and 150 gallons of (clean) water, powered by gravity, now come out the clean out...... into my face........
I learned from that.....