Reply #3: That diagram is very helpful

[Stinky The Clown]

I tend to agree with your initial assessment ... there may be a clog in the thing you label 'metal pipe' ..... the horizontal between the sink drain and the stack.

Don't worry about the height of the stack. That's not the issue. And relationship of the sink drain to the stack is such that you probably have enough venting that it should work. It isn't ideal, but it's probably okay.

I'm also worried about the joint between the sink drain and the 'metal pipe' portion. That should be fixed. That said, there's no need to worry about a pressure-tight connection in a drain line. They're only ever exposed to atmospheric pressure, which, in the pipe, amounts to zero. But it should be watertight to prevent leaks. Leaks (particularly in areas hidden from view, are **not** your friend. they can lead to huge damage.

But ... what can we try to fix the immediate problem?

I actually think I'd start with a strong chemical. The most potent drain cleaner you can find. If you can see the top of the 'metal pipe' above the floor, pour it (slowly - carefully - very, very carefully) into the pipe and allow it to work. It will need flushing afterwards, so after you pour, reconnect the sink drain. Then wait the prescribed time and flush as per directions (warm water is usually called for).

Now ... a few words of caution. First, drain cleaner is potent stuff and not to be messed with. Keep the kids away ... and that means in the basement below the pipe, too. Sometimes, drain cleaners get the clog loose, but don't break it up. the clog just moves further downstream and forms a new clog. Not often .... but it happens. That new clog, being further downstream, could be both harder to reach and harder to clear. Kinda like a thrombosis.

Also, if you later decide to snake the line (if the drain cleaner fails to dislodge things) you'll be pulling the drain cleaner back out with the snake. That could be unsafe for you if you get drain cleaner splashed on your skin - or worse, in your eyes. I don't suggest you use drain cleaner and then a snake to follow up. As just said, it can be really dangerous to do so.

And always have the area ventilated.

If you want to tray the snake route instead of the drain cleaner route, then start the snake where the sink drain is removed from the 'metal pipe". Any snake can absolutely turn that 90 degree bend. If it doesn't, that may well be your clog. And some clogs are hard as bricks.

Now, you said this first showed up when your kid dumped cereal down the drain. That could certainly cause a clog in an already marginal drain. But it should also clear easily. In fact, just having water standing behind it should dissolve it in time. As of now, is there **any** draining or is water standing in your sink like a stoppered bottle? If it is draining, but very, very slowly, drain cleaner could be the better choice. If it ain't movin' a damned bit, you may want to go for the snake .......

Lemme know how this little bit a Saturday morning diversion goes. :)