I'm not sure how the reproducible builds machines works for forcing two different build results, but i'd bet they're using sbuild too.
Here's a diffoscope of one of my packages which is not reproducible right now[2].
I also highly recommend the reproducible builds talk at this year's debconf with the repro build folks[3].
[1]https://wiki.debian.org/sbuild
[2]https://tests.reproducible-builds.org/debian/rb-pkg/unstable...
[3]https://debconf17.debconf.org/talks/14/