Essentially what happened was this:

Back in June, the city of Modesto was doing some routine maintenance on the sewer line which runs down the middle of the street in front of our house... a process involving an rotating auger to cut roots growing into the terra cotta sewer, and pushing the resulting root ball to the nearest manhole cover to be extracted. A root ball, however, was inadvertantly left lodged in the line approximately 15 feet past the connecting sewer line into the house. Consequently, over the course of about four days, with the rest of the neighborhood continuing to use their "facilities," the main sewer line backed up until it reached our line and overflowed our facilities. The resulting "sludge" is what you see above that had flowed from the bathroom to the rest of the the lower level of the house in about a 30 hour period (note the reflection of the overhead lights on the floor). Fortunately we had a friend, who was watching and taking care of some routine chores during our absence, discover the mess and the city and related crews were called in to stop and begin the cleanup. If the sewage had continued to flow undiscovered for 72 hours, the entire house would have been unsalvagable.

Be advised. These are disgusting pics: toilet overflow | bathtub overflow | what happened