Go to UK census collection on Ancestry. Scroll down until you hit "ssearch a specific UK census by year"
Scroll down to IOM 1871 andclick on it. Scroll down to "please chose a civil parish" You will see [Douglas] as one of the choices. Enter that. Then you will see "please choose a sub-registration distric"t. Click one.. I started with E. Then click on "view description of enumeration District"

Wouldn't you know the first street name that comes up for e.d. Douglas E 9a is "Drumgold Street". Look up at the top of the screen and click on e then "district 9a which takes you to page one of the E. D. which happens to be Drumgold Street. Looks like Ancestry has flubbed because e.d. 9b shows the same description for the enumeration district as 9a and I went through the eleven pages and didn't see a Drumgold. But practice with it and you'll see you can Browse the district by street name and housenumber.