Several days ago, an open overflow pipe in our basement started to overflow and release water with food particles and other sediment onto our basement floor. Then last night, our kitchen sink (which is above the basement and apparently tapped into this line), backed up completely on both sides (it contains a garbage disposal on the left side and a regular drain on the right). This also contained quite a bit of food sediment and sludge.

I applied drano gel to both sides of the sink, and after about an hour, they did clear. However, when checking the overflow pipe in the basement this morning I noticed that this pipe is still overflowing with water (although not continuously). The water coming from this pipe also appeared to contain some of the drano product in it. Also, while the kitchen sinks are drained, if we use them they still eventually back up again and drain-but very, very slowly.

Also--and perhaps most importantly-- none of our other bathroom sinks, toilets, shower drains, and washer-dryer hookup are affected in any way by this (no backups or overflows, etc. in these areas). The floor drain in our basement is also draining fine, too.

Is this a clog somewhere in the line in the to/from kitchen sink? And should I continue to try to clear this by further applications of either a gel or foaming drain cleaning product, or will it have to be snaked out? Or will something else need to be done? Any suggestions you could offer would be much appreciated. Thanks!