My brother in law installed a toilet in his basement. Everything seems find, except that now the toilet on the 2nd floor works, the toilet in the basment works, but the toilet on the first floor won't flush. He took a shop vac up on the roof thinking he needed to clear a bird nest out of the vent pipe. THere was no bird nest. He did find out that while he had the shop vac running the toilet on the first floor would flush. What has he done wrong?
Norm