Aww, crap.

I notice that the sewer is backing up, spewing sewage out of the new floor drain and filling up the downstairs bathtub. I inspect the sewer cleanouts and discover that the main sewer drain is getting plugged up somewhere between the house and the street, probably somewhere under my front yard.

Sewage spills out of a newly-installed floor drain with the paper seal still on it.
Shower control parts sit in an empty bathtub that is backing up with sewage.