Toilet/waste drain issue

Hi... just bought a two-story house with 2 bathrooms (one upstairs and one on the main level)... upstairs toilet works fine but main floor toilet would not flush anything but liquid...the smallest amount of paper or waste would prevent evacuation. Upon taking the ceiling out of the basement underneath the toilet, I found that the flange dropped down about 5 inches where it was met by a 90 degree elbow... it then ran about 3 feet in length horizontally to where it disappeared inside a wall (I could see however that it took another 90 degree bend dropping straight down... where it goes after that is anybody's guess. I can tell you that the main stack is about 10 feet away from the rough-in, in a straight line). The BIG PROBLEM I noticed, is that the 3 foot horizontal run actually slopes slightly upwards (against gravity). Is this why my toilet won't flush solids (and water tends to flow back into the toilet on liquid flushes?) If so, what do I do? And what is the proper rules for the slope of a toilet drain? P.S. I know it can't be the toilet, because I replaced the old toilet with a new toto gravity flush (the carusoe) and it does the same thing! Thanks for your help (I'm a complete novice). - Toronto Dion

toilet

A slight uphill slope will not cause your problem unless the total amount of backpitch created a "pool" under the toilet as deep as the pipe is wide, which is unlikely. You may have a drainage problem, but if so it is something that we cannot diagnose from here, not being able to test the toilet or see the piping.