A global thanks to everyone that responded and tried
to help. After climbing up onto the roof and checking
the vents, I decided that there was no way I was going
to safely make it up with the snake. (About 45 pounds
dead weight.) So I called a plumber. He did the roof
thing and appeared to put a truckload of snake down the
vent drain. Nothing. After checking the main sewer clean
out, we discovered that water was backing up there. So
another truck load of snake went down that, and there
seemed to be a problem down there. After measuring the
length when it came back out, we have to call the city,
and the cable company that dug up the lawn two weeks
ago. At least I might get back my money for the plumber.
Just don't realize how much we miss the grungy sewer
until we need it.