Kitchen Sink drain problems

[irish81449]

:wall: Live in split level home. Kitchen sink on ground level is slow to drain. Have dual bowl sink. One side for washing the other for rinse. Disposal on rinse side,dishwasher drains through disposal. When I run the water on either side after 15-30 secs. water backs up into the other bowl. When filling up both bowls with water and releasing stoppers at same time water drains very slowly. When I run the disposal, water enters up through the other drain. I rented a 50' drain auger. Snaked out the entire 50'. No difference. Changed drain plastic piping including diverter tee from disposal. Again no change. Took 5/8" garden hose and stuck end down into drain pipe under sink. Let the hose run for 15min. full pressure .No change. I looked into the vent stack on the roof and no visible blockage. Even took garden hose to roof and ran water down vent for 5-10 min. The kitchen sink has no visible vent stack above it . the vent is over 2nd floor bath. The kitchen sink drains straight down through 1st floor into 3" plastic pipe in crawl space and then is buried into ground. I find no visible cleanouts or vents. No other drains are slow in the house. 2 toilets and 4 other sinks drain fine. No sewer smells or anything from other drains. Like I said I snaked with 1/2" auger full 50' 4 times.
I am stumped . Help !
Bill from Ohio

[majakdragon]

Sounds like a venting problem, or lack of. I have included a link for an Air Admittance Valve that shows how they are installed. Drainlines need air to work properly and your set-up does not seem to be correct. Good luck.

http://www.studor.net/