What happens if a person recieves a free sample of chamets on peasach?
Best to have in mind not to acquire it to begin with, and throw it in some garbage can that's not yours.
Otherwise, flush it down the toilet ASAP. (Well if it's chol hamoed you could burn it, but probably faster to flush it.) Note: you may have to break it into smaller pieces, or smaller batches, to flush it properly.