Insufficient fall in a waste line — when a bathroom is below grade, or below the public sewer — means the home's waste line can't use gravity to transport sewage out to the city line. Instead, the home needs a sewage ejector pump, a system that relies on electricity to pump waste upwards and to the street. I see these all the time in the hills, when below grade areas are remodeled into living spaces. Power outages are a big bummer 👎🏼