Regressions happen. They suck, but they happen. My son went through a regression when he started school...he would poop his pants during naptime. It was embarrassing because he had been trained for over a year, and it really stressed us out. There isn't a ton you can do about it other than continue to encourage the child and offer LOTS of praise when they do good. When they have an accident refrain from showing you are upset or frustrated. It will only make things worse. Accident = oh well it happens! At their age you could try a treat/ toy at the end of the day if they keep their pants dry. As far as cleaning poop accidents, no way! Dump in the toilet the solids and the rest goes in a plastic bag. No rinsing. That's the parents job and honestly it's not sanitary to be rinsing poop in your sink, even if you disinfect after. Honestly sometimes when my son had poop accidents and they were too soft I just threw the undies in the garbage. Just gross lol