It doesn’t take the brain of Britain to work out that pouring semi or completely dry faeces combined with sawdust, car litter or similar as the potential to create a blockage in a system not designed to take such items. Just because the members of this forum cannot, hand on heart or a sty of Bibles, you choose, cannot prove categorically that this has happened doesn’t mean that people abusing the waste facilities wont (or haven’t already) caused a blockage. The chance of the culprit a) admitting to their folly, or b) hanging around to help Dynorod (substitute with appropriate drain clearance operatives as appropriate) are slim to bugger all.
Just because it hasn’t happened yet doesn’t mean we shouldn’t plan to avoid the scenario.
Compare with a nuclear Holocaust, we haven’t had one but we should do all we can to avoid one.