My daughter bought an old house that had the sewer drains and sump pump replaced five years ago. I stopped by yesterday to look at what she said was water pouring out of a pipe. Closer inspection shows the sump pump kicking in when she uses large amounts of water..bath tub or load of laundry. I followed the main drain/stack to the basement and it terminates below the slab adjacent to the sump pump. I couldn't get the lid off the sump so I will try again this evening with sockets but my question is...I thought the lines were completely independent; drain lines emptied out into the sewer and any excess water in the basement gets routed to the sump line out into exterior..? Can a partially occluded main sewer line cause a backup into the sump below the concrete when high volume of water is being drained? I don't smell anything such as raw sewage, fecal matter, or anything else in the sump. Thanks in advance for the feedback!!!