I dread what my kids will help me to add to this list.

cat litter made from clay/silica can build up in the pipes after a while.

Thank you! Condoms are bad news for drains. Please don't flush condoms!

Thanks for the suggestion on the back flow preventer. We have one but the problem happens when the connection gets clogged and there's nowhere for "new" sewage to go and the plumber has to snake it out. I guess this means opening the back flow preventor and then all the stuff that's behind the clog rushes in. Regular snaking is key but dang it I wish people would stop flushing inappropriate stuff. And I wish the MUA would educate people on this topic.

dead mice & goldfish

The hopes and dreams of a generation.

Baby alligators.

Condoms.

We found a slew of them when they had to pump out the line connecting the building to the sewer main at my previous home. Someone was sure having a good time! As it turned out, that connecting line was 100+ years old and made of clay. It had collapsed, requiring a costly replacement. The good news was they replaced it with a PVC pipe that had this hinged trap so that sewage can only flow one way - away from the building. You might want to look into that for your home. Costly, but worth it, imo.

Well, once again the floor of my basement is covered in sewage. This time the connection between our building and the main was all plugged up with tampons. As no one in our building flushes those I know the problem originated somewhere else in the neighborhood. Previous backups were caused by cooking grease and paper towels.

Please don't flush:

tampons
tampon applicators
paper towels
q-tips
"flushable" wipes (the ancient JC sewage system can't handle them)
cooking grease (or put it down your drain... throw it in the trash)

Anyone want to add to this list? What else have you had problems with?