Welocme B W Freas:
If you are going to use chemical drain openers, please don't call me to repair the plumbing. Many of my friends have suffered acid or chemical burns because the customer tried them first and they didn't work. The more seasoned plumbers know their customers will use one or more chemicals before calling them; they also know the owner will say they haven't used anything, so they watch for it anyway.
Inspector D is correct, you have an obstruction and the lowest drin is backing up. Keep using the drain and it will back out on the basement floor.
In this case, it would be best to call the plumber for the repair and watch him as he works; then you will know what to do the next time.
My sewer (the line to the street) has had roots reamed out of it 3 times before I finally figured out I could keep the roots killed out with salt. I went to the Home Depot and got a bag of salt pellets like we use in a water softner. I add a cup on the first day of the month and the pellets hit the roots and lodge there disolving into salt brine which kills the roots, they break loose and float on down for the city to contend with.