I've been trying to fix a extremely slow draining bath tub for awhile, but still can't get it right. Here is the work that's been done:
Ran 25 feet of cable from a power snake (drill powered) 3x's. Results: some black gunk on about the first 12 inches of line and a few strands of hair. No change.
Plugged the overflow valve and plunged the hell out of it. Results: (this is interesting) removed 2 handfuls of acorns that the local Woodpeckers deposited down the roof vent! I continued until no more could be removed. No change.
Pushed an expanding pulse bladder down the roof stack about 7-8 feet and ran it for 5-10 minutes. Results: no water backed up from any other drains. Opening the nearby clean out I could hear water running! But still No change.
The sink that is in the shared bathroom drains perfectly. There's a clean-out 5 ft. outside the window. I've opened the wall were the drain is located, but it takes a direct 90 into the slab. One of my guesses is the drain stopper used to plug the drain for a bath some how broke off from the lever. It's an unbelievable plumbing problem that has me completely stumped.