Lived in or right outside DC most of my life and have had many half smokes. As far as I can tell, you start off making a half beef, half pork Kielbasa. Make sure it's at least half fat. And cut the seasonings by at least half. Then smoke it for a half hour. Then simmer it half the day in a vat of greasy, dirty water until it's half green. Then put it on a half stale bun.
Seriously, the half smoke isn't half bad. It's all bad.
These were pretty much all DC had to offer street food wise back in the '80s, and they were usually cheap, so we'd eat them after the bars closed.
I'll check and see if the local grocery has any next time I go, and if they do I'll snap a photo of the ingredient list.