Help me explain why up stair toilets drain but down stairs doesn't drain

Ok, so the two toilets up stairs work just fine. All drains in house are not an issue. However, the downstairs toilet when flushed does not flow out the water in the bowl.

The toilet downstairs is only about 4 feet from the main sewer connection to the foundation. I've snaked 15 feet of the line from the toilet to the sewer and found nothing. When I took the toilet off the flange there wasn't water in the drain until about 8 to 10 feet down.

So now I've got to explain why all the other drains work fine if this one is an issue. I was told that if this is the issue wouldn't the water level in the downstairs toilet raise up when we flushed up stairs toilets or ran the washer, ect.

Could it possibly be that the vent line is clogged for some reason? Please help me understand why you have told me the sewer line is blocked if everything else works.

Thanks,
Ryan

Maybe a toothbrush, comb, pencil, pen, toy, etc. stuck inside of the toilet itself.

Eh, I checked the toilet. I also bought one of those toilet auger. The kind with the 90 degree plastic cover so that you don't scratch the bowl. I ran that down and Thur it first before I bothered to remove the toilet and snake the whole line.

Doesn't mean there's not something still stuck there...it could easily go right by a pencil, but when flushing things with paper, gets hung up.

With like the augers with the bigger ends.
The small ones miss too much.

toilet

There could be any of several reasons for your problem. If there is water in the drain line regardless of how far down it is, and there is a lack of venting or obstructed venting, the toilet will not flush, as one possibility. We would have to be there and make our own tests to determine the cause and cure, if any.

How do you check the vent tube? Do you go up on the roof and have someone flush the toilet and see if air gets sucked down?

Thanks,
Ryan