I cannot find the sink either. I have only the stickers from the first level on my trunk, and I haven't gotten any other decals from this episode. I've seen the balloon and the tire. I just have no clue where to look or what to look for. My eyes hurt from trying to find anything while the buildings are moving
Edit: Finally got it. I had to get the other decals in order for it to appear. It's thrown off from very high up, so keep your eyes in the roof area of the tallest building on the right side and it should soon enough be thrown out from there.