After trying bleachbit, which trashed my whole system, I had to reinstall.
Captain_Chicken, you've joined the club!
Not a pleasant one to be a part of either, as myself & I believe Nick has had similar results. BleachBit is a dangerous tool to be using, as well as 'Computer Janitor', another like tool in the Software Manager. This is why we don't recommend cleaning tools for Linux, no more than we recommend registry cleaners & 'tune-up utilities' for Windows. All are lethal tools to be using.
Linux installs doesn't take up massive space with unused Temp System files, maybe 300-400MiB, if one is that low on drive space, time for a new one. My root partition is 40GiB & uses less than 9GB of it. The real garbage is in the /home partition, where BleachBit doesn't reach, if one uses the same /home partition for a few major releases after not formatting, there will be 5-15GiB of garbage, some files no longer compatible with what one's now running & affects speed. I found this out when installing a larger drive to hold my virtual machines in /home, wow what a mess of files there were on the old /home partition after examining once I got my system back up & running. It had been used since at least Mint 12 (possibly 11) through 17 & still going. At any rate, there's a lot more on the /home partition than those dozen or so folders we see on the desktop. It's also where many of our configuration files are stored.
To avoid a mess of files being transferred to the new drive, copied everything needed to an external (NTFS is fine), installed the new HDD, formatted half of the 1TiB HDD as /home, created various Windows data partitions, and left 4GiB for Swap at the end of the drive. Then post clean install, copied my personal folders back over, including my VM's.
Later on, before wiping my WD RE4 500GiB HDD that had been a combo of Mint /home & Windows data, deleted all of the content in the folders, and there was over 14GB of data left! Used some Search tool to examine the contents, some had dates of close to 4 years back. That drive came out of my prior PC & into this one, so had gone through a lot of 'fresh upgrades', just formatting root, and assigning /home & Swap, but didn't format over. Had I known what I then did, would had moved everything prior to every major release, formatted all, and copied the good back over.
Point being, if BleachBit was worth it's weight at all, would also had cleaned up much of that clutter, yet who knows what damage would be done in the process. That's where the real garbage was, not the few hundred GiB's of Temp files in root.
Now you know by firsthand experience, to leave BleachBit alone. If you wish to clean up anything, your browser's cache is a great place to start.
For the most part, the Linux root filesystem does a good job of cleaning up behind itself.