Okay, I am a plumber. We got two connector things at HD today and went down into the dungeon armed with a hacksaw, a five gallon bucket, a 8' section of square tubing, a 4' section of a broom handle, a screw driver, and a deburring tool.
Cut into the plumbing right by the t where the wash machine comes in at. Established that water was draining fine through there and through the kitchen sink.
Cut into the plumbing right in front of where it joined the old iron pipe two feet before a 90* elbow that dropped into the main sewer line. That two feet was so blocked that we had to pound on it with the square metal tubing. Finally got stuff breaking up a bit and we were able to scoop it back out into the bucket rather than pushing it toward the elbow.
Then we took the garden hose and finished cleaning it all out to make sure that from the elbow to the sewer was clean too. (Used the hose like a snake.)
Who know how many years of build up was caused because of some very rough edges of where the pvc met the old iron pipe. SO GROSS!!!! and the smell...
But, we did it. Deburred all 4 ends that needed to go back together and then got cleaned up. Proud that we did it but I for sure don't want to be a plumber when I grow up!