I have a 60 year old house with a basement floor drain that has backed up twice in the last two days. No rainy weather, and the first time no water usage before backflow began. In both instances the water left the same way it came, through the floor drain. Can anybody explain how a clogged house sewer line could cause thisnd what would cause it to drain as quickly as it seemed to have done? I know I’ll be calling a plumber, but I just wanted to get some understanding. Thanks in advance for any explanation.