Thinking it might be the garbage disposal, I took it off, and checked it out, but it looked fine. I also cleaned some gook out of the S-trap.

So rather than re-attach the pipes, since I had easy access to the drain, I took the water line off the faucet, put it right into the drain pipe, and turned on the water pressure. Sure enough, it ran for about 30 seconds before clogging. Five minutes later, with a flashlight, I could still see the water level; it had only dropped about 8 inches.

I went and got my 25' auger. After 8 attempts, I did clean some gook, but it still not unclogging!

Underneath the sink in the cellar is a 90deg elbow, 18" of 1.5" diameter copper pipe, followed by a 45 degree elbow, followed by 6' of the same pipe, which then goes into the main waste line. The 6' segment is soldered at both ends.

While I am familiar with basic soldering of pipes, I'd like to know if I can just remove the 6' section, and what I'm getting into here. Can I handle this, or is this a job for a pro? Any ideas what this could be?

Thanks in advance!

Beyond that, what kind of disposer is in place? If it's a small economy model or very old, it may not be grinding very thoroughly. Years ago I lived in a place with a cheapo Insinkerator Badger disposer. It seemed to work just fine, but I was constantly plagued with a clogged drain line. I finally replaced the old, cheap disposer with a 1 HP top-of-the-line Insinkerator. The more powerful units have much better grind elements, spin at a much higher rpm, and grind food into much smaller particles. After the replacement, I never had a stoppage problem again.

Since that time, I've become a landlord. When I've had recurring problems with clogged kitchen drain lines, I change out whatever disposer is in place with a 1 HP model. After that, I seldom have problems again. IMO, spending more for a good disposer saves money. Roto-Rooter is expensive.

I'd say you need a plumber to resolve the vent issue.

What I DON'T get is all the other drains are fine (there's a bathtub on the same floor), and how much water could it POSSIBLY take to "block up" 8'L x 1.5"W pipe!?! That just doesn't make sense to me. The neck on a bottle of soda is tiny compared to a 1.5" diameter pipe. SURELY there's plenty of room for air to come in!

Here's a thought: Perhaps the drain pipe is not at a proper angle to drain. Could that do it?

If it IS greasy/gunky/foul smelling, then I'd try a chemical drain opener, but only after the line has had a chance to drain. (think how you'll pour it in there, too - might be tricky)

As far as cutting the line, I'm sure you could probably do it (once other remedies are exausted), and provided you plan what's next. You can reconnect the piece with banded fernco couplings or you can replace the piece with PVC, if you like.) (Don't do this if there's chemical still in the line.)

Start with snaking again - hopefully that will clear it.

I'm not a plumber, but as I understand it, water running at full strength can overwhelm the drain. when that happens air can't escape from the drain line and a bubble builds up in the drain pipe. The bubble tries to rise up through the pipe, but increasing pressure from water building up in the drain and sink won't let it clear and may even push it back down the line.

The bubble has no place to go for escape, except through the drain opening, but the pressure created by water passing through the drain and into the pipe is pushing down on the bubble, keeping it in place. Even after the flow of water into the sink stops, the weight of the backed up water is bearing down on the trapped air bubble. Until enough water can trickle past the bubble to lighten the load holding it in place....the drain is stopped up. Once the pressure from trapped water lessons enough for the bubble to push past it and escape (it's sort of like a burp), the drain will flow freely.

A properly vented drain won't have this problem. The displaced air will be able to escape through the vent line which won't have any oncoming water or pressure in it to impede its escape.

-- What do you mean by "8 attempts" at snaking? Do you mean that it took 8 attempts to feed it in there once?

I mean I fed the snake a few times, and got some minor "gook" out. I then withdrew and reinserted it about 5 more times, felt it hit something solid (approximately the right length to be hitting the main vertical drainage pipe), twisted it around, withdrew it, and found nothing stuck to the end. I did it again a few minutes ago, and it came out clean again.

-- Try the plunger again.
Plungering for a few minutes will free it up, but it always seems to clog again

-- Is the bathtub drain vented or near the main vent stack?
It's very difficult to tell, since the other drains are practically up against the floor above me, but it doesn't appear so. If it is, I can't see it.

-- Possibly the vent exists but has not been recognized/identified.
I just still can't get over the fact that the other drains would be connected to this vent, but the kitchen sink wouldn't, considering the drain pipe terminates within inches of all the other pipes. Logic would suggest that there is no vent, so therefore why is there no other problem, such as with the bathtub drain, which is on the same floor and within 15 feet? Draining a bathtub would overwhelm the drain a heck of a lot faster than the kitchen sink, wouldn't it?

A kitchen sink, on the other hand, is very often some distance (more than a few feet) from the main vent stack. Because of that, it requires a separate vent to ensure that it remains free flowing if the drain in the sink is overwhelmed. It makes no difference if the drain pipe terminates within inches of the other drain pipes. If air pressure can't equalize in the pipe, it's not going to drain properly.

Since you don't seem to understand the purpose of proper drain venting, I suggest you read the "Purpose" section of the Wikipedia article at the link below. If you're still not convinced that you have a venting problem, call a plumber. Perhaps he or she can explain your problem by pointing out the apparent inadequacies of the existing waste water system.

My friend called the previous owners of the house (friends of her father who retired and moved to Florida). They only owned the home for six years, and said they never really had a problem with it until recently, maybe six months before they sold. They would just plunger it and leave it alone.

So being that it looks like this house was built in the '50s or '60s, and apparently does not have a vent, I'm left with:

a) Why doesn't it?
b) What would cause it to operate fine for at least 5 years without a problem, and then act up suddenly?

I'm going to take another look at it today and see if I can find a vent -- any vent at all. I found the main sewage pipe, obviously, but there was no vent next to it. I'll bring my camera and take pictures, in case they'll be of any help.