It took advantage of the Coanda Effect in order to get the exhaust plume to the diffuser. It featured a ramp in front of the exhaust which started below the exhaust tip and ended almost in front of the diffuser.
This is what the exhaust ramp looks like:
By race 5 though, they changed their exhaust layout and opted to use a solution similar to the McLaren one. (Drawing below)
This layout was better because the Coanda ramp was not attached to the floor so there was space for air to flow more easily to the diffuser and produce more downforce, while still taking advantage of the exhaust plume.
So why would the want to use their older solution since with the newer one they could blow the diffuser AND get cleaner airflow to it? The older solution provided a smoother path for the exhaust plume to follow and was more predictable and easier to understand. Red Bull though in an attempt to get the best of both worlds, created a tunnel below the ramp so effectively created a bridge for the exhaust to follow and for air to pass underneath that bridge. This though proved hard to get right and took them the first third of the season trying different solutions and even closing the tunnel in Bahrain or completely scraping blowing the diffuser in China on Vettel’s just to get a comparison.
What Sauber has done in their latest interpretation, is make the ramp a bit thinner at the point it meets the floor to get cleaner air flow, and provide a smoother path for the exhaust plume to follow. In addition after Jo Bauer accused Red Bull of using an illegal engine map in Germany, teams were forced to choose and use an engine map that was used in the first 4 races of the season, the period when Sauber was using their old solution. This is how the new exhaust looks like:
Also here is a comparison between the three interpretations with their first exhaust ramp, their McLaren like exhausts and their latest solution, 1st, 2nd and 3rd respectively.