They sell these in dollar stores here.

I didn’t have to unclog a sink for years and didn’t own a plunger. I was looking for a “classic one” but they only had these and I wasn’t sure. I gave it a try anyway and to my surprise, it was very efficient.

Never tried on a toilet and I suspect it would work fine too, but I tried it on my bathtub drain and unfortunately it fails to make a seal.