I have a small house with e sinks back to back (bath & kitchen) and then the toliet and tub all on the same wall maybe 6 feet with the sewer line in the wall. For the last 3 months the drains are running slow when you run the water th sinks back up and take a while to drain and when you do you get a gurgle once they clear. I have used drain openers gels, liquids and build up types and the drains still run slow. It is a 2 story and the air line I can't get to to look down it to seee if it is clunged up. I have pour these drain openers in a gallon at a time leave for 8 hours or long over night I run hot water before I pour it in and then boil water and pour it in after it has been in there the time period and yet I still have slow drains that gurgle when they finally clear. I have replaced the cast line in the basement about 8 years ago because it rotten thru. Can't access the line in the wall but it is galvinized I think and should be good being it is maybe 6 ft long total.
The house is about 70 years old. What is causing the gurgle and slow drains and is there anything I can do to correct this being the sinck drains are smaller thah the line in the wall so snaking does not seem to be effective either.
Culd the air stack thru the roof getting clunged up?
Any suggestions would be helpful.