Drain backing up?

[Bullhead]

Having problems with my kitchen sink backing up. Have snaked the whole drain Down to the 6 inch pipe. used draino gel and other drain cleaners.
Replace the Sure vent with a new and it still backs up. it is the only one that backs up. Not sure if it is an air lock or what? Wondering if the clean out pipe could be the problem? Anyone have any ideas?

 

[phishfood]

You could possibly have a soft grease clog. A snake can pass right through that, and the grease will reseal itself.

 

[Bullhead]

How would i get rid of that?

 

[Geofd]

have you tried using the sink without that vent on it??????

How would i get rid of that?

boiling hot water