My kitchen sink has long been a pain. The builder went cheap and instead of venting the kitchen sink to the rook they installed an under sink vent valve and that seems to be the cause of many troubles. It seems like the vent begins to whack out and then the drain will start to run slower and finally back up, thus I usually have to both hog the drain out and replace the vent. This week it happened again (in time for the holidays - yea) and I snaked the drain (found very little) and sure enough it would still back up within 15-30 seconds of running the water. I can loosen the vent valve and it will break the vacuum and the water will go down, so once again and replaced the vent (Ventmatic or Pro-Vent product) but with the same results although the vents (both old and new) seem to operate fine in that they aren't bound up or anything. One of the installation sheet that came with a vent years ago indicates that the height of the vent above the trap is important so I have raised it up to where the vent is now above the bottom level of the sink and this time I have tried different heights without success. There is obviously a vacuum in the drain but not enough it seems to open the vent valve. Please does anyone have any insights on this?

Time to replace the vent with one that works. We use mechanical vents on a remodel job where we can't get to the roof or attic to vent the fixture. NEVER on new construction. Having said that, keep the vent above the drain line of the sink and replace it. I have a mechanical vent that I've lots of luck with. Check out Studor Mechanical Spring Loaded Vents at;
http://www.studor.com/homeowners.htm They are manufactured a few miles north of where I live and the nicest thing I can say is that I've never had to replace one. Good luck and Happy New Year, Tom