Emptying Trash Increases System Storage?!

Hi all, I'm desperately trying to clear some space on my hdd. I am monitoring my system storage. And it seems that every time I empty the storage bin, the storage allocation doesn't free up but rather does into the mysterious "System" category! I've cleared about 30gb and it's all going into System. I am so perplexed! How do I get the system to clear these files permanently. Nothing seems to be freeing up storage.