Pat Cummins has called for improvements to the third umpire system after Australia saw several key wickets slip away in their third Test draw with South Africa.

The hosts were denied a clean sweep in the three-match series after they tied with the Proteas at the Sydney Cricket Ground on Sunday, with a rain-affected match hampering their hopes of a win.

Australia had two catches overturned by third umpire Richard Kettleborough after the ball was judged to have touched the ground following numerous replays, while South Africa were also denied the wicket of Marnus Labuschagne on day one in the same manner.

Cummins was less than impressed with the process, though refused to blame Kettleborough and instead speculated over what could be done to help the third umpire.

"I don't really know the answers, but there has to be a way to try and improve it somehow," he said. "As it currently stands, it's really hard to give a batter out.

"If there's any kind of benefit of the doubt, it goes the batter's way. I think with a couple of camera angles really slowed down, it's pretty hard not to find doubt somewhere.

"I do feel for Ketts a little bit up there. Maybe there's more cameras we can use down the track. Surely there can be some small changes we can make."

Steve Smith, who was denied a catch for the second time in the game after Heinrich Klaasen was edged to him off Nathan Lyon, echoed his captain's sentiments.

"Yesterday, I was a bit more uncertain than today," he added. "I was pretty certain I got underneath the one today.

"I think those ones that are close to the turf always don't look great. But today I felt the slap on my fingers and I knew I was under the ball."