Thanks for all the replies. My interest is twofold. First, I just don't like the unfinished look of the open tube ends. True, they don't end bluntly and they are a bit rounded, but still, I think closing off the openings would look better. Therefore, "practical" solutions such as rubber lab stoppers and silicon tube nozzles don't much appeal to me. Second, these kinds of openings are very attractive to wasps, hornets, and the like looking for a place to set up housekeeping. I'd just as soon discourage them. I have wondered whether the closed off tubes would retain water, so I would prefer a closure that isn't completely air tight.
Still looking for suggestions. Thanks.
