It was a very brief mention.
Most people don't decide to pay or not pay taxes based on perception of corruption, but rather what they perceive they're receiving.
In Canada, we generally are content to pay taxes because we get such benefits as free health care, cheap medicine, free primary and secondary schooling, subsidized post-secondary schooling, and our cities are generally quite clean with good infrastructure, which is a good accomplishment considering our population density is very low.
My wife is from a third world country where almost no one pays taxes. Then again, what do they get? Infrastructure is non-existent (roads are all gravel or dirt, power is on about 50% of the time, no potable running water, police are non-existent, etc...). This is the conundrum of development economics - how do you go from this stage of development, to a new stage where people pay taxes so the government can provide services? With no services people will avoid taxes, with no tax money the government cannot provide services. The answer of course, is that it's difficult and takes time.
Corruption is an easier problem to solve, but difficult to implement. To get civil servants to stop accepting bribes you need to pay them enough that losing their pay is actually a punishment, or punish them enough that the threat of jail time counters the benefit of accepting bribes (or ideally, a bit of both).
Anyhow, neither problem can be solved in the amount of time that the troika has expected Greece to solve them - and they ARE economic problems, not moral ones.