Please forgive me if this isn't in the correct forum - I didn't see one specific to kitchen sinks.

Let me just start off by saying that I can not afford to pay a plumber hundreds of dollars unless I really can't avoid it, so I'm trying to fix the problem myself. Of course, I could end up having to do that anyway, on top of all the money I've already spent in DIY stuff. lol

So, here's my issue:

My significant other and I moved into our current home in January. The previous owners are sort of stupid in the way they did things in terms of renovations. We did a lot of painting, and rinsed the brushes and everything in the kitchen sink (which I've always seen people do so I didn't figure it would cause any problems in the plumbing as long as I flushed the pipes well afterward). Sink was behaving fine until a few months ago or so, when it started backing up while I was washing dishes. I use a dishpan rather than washing my dishes directly in the right side of the sink, and rinse them in the left side. Thinking it was a minor clog caused by food lying in the trap or something of that nature, I mixed vinegar and baking soda in the drains and let it go. The clogs always cleared easily that way.

Then, it happened. My sink was possessed by some demon spawn from the depths of Plumbing Hell.

It started slowly, backing up just a bit and draining once the water was off. I kept forgetting to buy DrainO. Finally, it backed up so badly that it took nearly 30 minutes to drain small amounts of backed up water. We tried DrainO, no results. I took off the trap (U shaped) to see if the problem was there, and it was perfectly clear. Water ran from both sides of the sink just fine with the trap off, so I figured it was further down the line. We bought a 25-foot auger and snaked the pipes under the sink (and as far under the floor as the auger would extend) four or five times. Still not much better. Finally, a neighbor of mine brought over a Drain King (bladder type of doohickey that connects to your garden hose) and that seemed to clear the drain pretty well. I boiled and dumped several large pans of water down the drain afterward to try to flush out any ickies that were left. The neighbor thought that the auto trap vent (indoor, not roof top) may have gotten all gooped up, so he suggested buying a new one, which we did. Bought new mesh strainers for both sides of the sink. The sink was fine for a few days and then BAM! Backed up again.

We went out and bought our own bladder doohickey and used it, which again cleared the drain. More boiling water dumped in, followed by DrainO and the sink drained fine again for three days. Bear in mind that I washed dishes that evening, using the strainers, and have not washed dishes after that. So the only thing that's been going down the sink drains in the past three days is soap and water (from washing my hands).

Then, it clogged again yesterday while I was washing a fork (because I always wash them before I use them even if they've already been washed). SO, today, I cleared it again. Yet more boiling water, and a lot of boiling blood. Draining fine. Again. Until it clogs again. Which at this rate will be in four days. And then I fear I may cut the pipes into shreds with a hacksaw just for the sheer pleasure of it.

The pipes are PVC (1 1/2 inch, I believe). We have hard water. Am I forgetting any pertinent information? The kitchen sink is the only place having a problem - both bathrooms seem fine. Any suggestions? What could be causing it to run fine after clearing it and then suddenly back up again a few days later?

Thanks in advance for taking the time to look at this.