It turns out that "bong" has even more meanings than I realized. Here is my current list:
The newest one (to me) is the last, of which I have been apprised by a couple of readers from India. They say that it is slang but not pejorative. It is thought to have originated in the elite national schools like the Indian Institute of Technology. There is even a movie about Bengalis that uses the term in its title: The Bong Connection. It is one of a set, such as tam for Tamils, mallu or mal for Malayalis, and gult for Telegu speakers.
There is also a bit more to say about bong as a smoking device. In current usage it appears to describe a water pipe. The Wikipedia article, for example, is devoted entirely to water pipes. As one reader wrote to point out, that is not the original meaning.
Back then a bong was a wide tube open at both ends with a little hole near one end. A joint, or a pipe bowl, was inserted into the small hole, and the user drew in smoke from the other end with his hand over the end near the hole, releasing his hand near the end of his toke to receive a sudden insurge of smoke. What is today called a "bong" was then called a "water bong", because it was a combination of a water pipe and a bong.
This is consistent with my memory. I remember seeing non-water bongs of this type, though I don't recall using one. So, it looks like bongs were originally very wide pipes, and that the term was transferred to water pipes via the intermediate stage of "water bongs". The original component of width appears to have been lost: though most water pipes are fairly wide, they don't have to be.
This raises the question of whether there is a relationship between bong as a wide pipe and bong as a wide piton. I can easily see the term for pipe being extended to pitons. I don't know of any evidence bearing on this.
Addendum: Reader Mark Seidenberg informs me of the existence of still another kind of bong: the beer bong. This is a device used for chugging beer.