What would you suggest, is the best way to combat toxic leadership, when the majority of the COC up to the local IG office is corrupt?

Your question is a little muddled because Toxic Leadership and outright Corruption (which is a crime) rarely go hand in hand. It's also hard to give advice when you don't have any details, so I'll give you some general advice.

First, you better know what you want and be honest with yourself. If you want a continued career in the Army, then the best advice may be to just keep your head down, do what you're told, to the best of your abilities, while putting in for a change of station, so you can get out of there ASAP.

If you are looking for "Justice", start by analyzing the situation as calmly and clearly as possible. There are always two sides to every situation. Ask yourself are getting both sides of the story? or are emotions and friendships swaying you toward one side while ignoring the valid points of the other.

When someone makes such a broad statement as "the majority of the COC up to the local IG office is corrupt?" I tend to think its probably a vast overstatement. Corruption is hard work and most people are just too lazy for it. While one or two people can be corrupt its just not likely that an entire Chain of Command is. However, such things as Institutional momentum, strict compliance with regulation, or even the privileges that come with greater rank can easily be confused with corruption.

All that said, if a crime is being committed tell the cops and let them sort it out. If you are actually just having a disagreement with management styles or management decisions...guess what, all you can do is deal with it, take care of your troops and try to be a better leader by not making the same mistakes you are seeing now.

Can you elaborate at all? I don't have enough information to offer any sound advice.

I would recommend taking a step back and ask yourself is the leadership really toxic or are my expectations unrealistic? A lot (not all) Soldiers that complain about toxic leadership are usually because the Soldier is sub standard and just whining because they don't get there way. Its kind of hard to believe that an entire chain from Company all the way to IG can be so corrupt. But if this is indeed true then its in the Soldier's best interest to just keep there head down and just do their job. Do their time and then move on to another command. Without hard evidence there isn't anything you can do. If it becomes a real threat to Soldiers health and welfare then you can possible initiate a Congressional complaint. But the Soldier had better be sure he is right before it gets to that level because by bypassing the command it will create a whirl wind that they'd better be prepared for.