A small piece of plastic fell down the drain in our bathroom sink and made it through the trap. It is now logded in a corner piece of the pipe. I have tried snaking it out and using extreme amounts of drain cleaner but can't move the piece. I am looking for suggestions before I remove part of the wall to disconnect the pipe.

I do not understand what do you mean by saying "corner piece pipe". All fittings have bends that will accept quite large solids. General rule of thumb is: if you are able to flush it through the toilet bowl, it will be able to negotiate its way through drain pipe all the way to the City Sewer.

Once it passed the trap, you should flush the toilet several times. Also, fill tub (located in the same bathroom) to the rim and drain it all at once. That will move the cap to the main sewer.

Milo

The problem is not with the toilet, it is with the sink. The sink drain pipes have several right-angle bends. It also goes from a 1 inch pipe to a half-inch pipe. That's what makes it difficult to snake.

It also goes from a 1 inch pipe to a half-inch pipe.
The minimum size for a lavatory drain is 1 1/4". If you are saying that the drain reduces down as it moves away from the trap then that is the problem.
Show a picture.