It's either water or not enough chemicals in the drum. Water is tough. When I used drum processors, I took both ends off the drum, dried the inside using a lint free paper towel (Kimwipe) and then used a hair dryer to blow out & evaporate the remaining water. Same with the inside of the drum - wipe down & dry with a hair dryer.
I would do that before making the next exposure so that the drum would cool down to room temperature & not raise the temperature of the chemicals. That's the only way I know of to get the drum really dry.
Hair dryers are really okay to use in the darkroom - just make sure the one you use has a built-in ground fault interrupter circuit. All of them sold in the US must now have that type of circuit so that if you're dumb enough to attempt to dry your hair while still lounging in the tub & drop the dryer into the tub you won't electrocute yourself. Don't know whether the same requirements apply in Australia - shouldn't be hard to find out.