1Tb Hard Drive keeps filling up.

Also....

Purging local backups

Please note that although this doesn't affect your remote backup from Time Machine, this will get rid of the redundancy (at least until the next Time Machine backup) that a local backup disk will provide. If you need such redundancy or are worried about the recovery of your data then you would be best served to let macOS determine when to purge these files.

Start Terminal from spotlight.

At the terminal type tmutil listlocalsnapshotdates. 

Hit enter.

Here, you'll now see a list of all of the locally stored Time Machine backup snapshots stored on your disk.

Next you can remove the snapshots based on their date. I prefer to delete them one at at time. Once my "System" disk usage is at an acceptable level, I stop deleting but you can delete all of them if you want to reclaim all of the disk space.

Back at the terminal, type tmutil deletelocalsnapshots YYYY-MM-DD-HHMMSS , where will be one of the dates from your backup. This will be in the form of xxx-yy-zz-abcdef. Try to start with the oldest snapshot.

Hit enter.

Repeat for as many snapshot dates as required

http://www.thagomizer.com/blog/2018/03/27/cleaning-up-time-machine-local-snapshots.html

tmutil deletelocalsnapshots /  # deletes all the snapshots

Empty Space - it is suggested to keep at least 15%  to 20% of the Drive Total Capacity as Empty Space for good operations of the computer.

What is “Other” storage on a Mac, and how can I clean it out?

Free up storage space on your Mac

OmniDiskSweeper Safe to use

GrandPerspective 

How to delete Time Machine snapshots on your Mac

See used and available storage space on your Mac

Locate backups of your iPhone, iPad, and iPod touch

The final word from Apple on Managing the " Other " Category

Other: Contains files that don’t fall into the categories listed here. This category primarily includes files and data used by the system, such as log files, caches, VM files, and other runtime system resources. Also included are temporary files, fonts, app support files, and plug-ins. You can't manage the contents of this category. The contents are managed by macOS, and the category varies in size depending on the current state of your Mac.

Just to make this complete. This is what DropBox recommended (but that didn't make a difference in the end) :

How to purge Dropbox files:

Macintosh

Clear your cache on a Mac

1. Open the Finder and select Go to folder... from the Go menu (or press Shift-Command-G).
2. A dialog box should appear. Now copy and paste the following line into the box and press the return key: ~/Dropbox/.dropbox.cache
3. This will take you directly to the Dropbox cache folder:
4. Delete the files in your cache by dragging them out of the Dropbox cache folder and into your Trash.

Dropbox Business or team users: If you have two accounts linked to the same desktop, the name of your Dropbox folder will be appended with your team name in parentheses or "(Personal)," depending on the type of account. For example, if you were clearing your cache on a Dropbox Business account called "Organization" you'd see:

~/Dropbox (Organization)/.dropbox.cache

Source: https://help.dropbox.com/installs-integrations/desktop/cache-folder

Hello

I had a similar issue with DropBox and purgeable files remaining. I unauthorized DB. Deleted the App. Deleted the DB folder. Re-installed and then I wanted to locally store my 360 GB folder but got "not enough space warning" although it shows 500 GB free. So DB doesnt recognize that it is purgeable files. But also iOS gave me update issues with "not enough space" until I deleted more files.

I already stopped TimeMachine (external SDD) and I executed the delete of local Snapshots as mentioned above. I found 3 and deleted them. But still I see this purgeable files that I somehow can't get rid of.

I think this is caused by DB and a real issue.

DB also didn't help other than delete it all and re-install which I did.

I even purchased a cleaning tool but that didnt solve it either.

I thought maybe an overwrite over free space via Disk Utility or de-fragmentation.

But both are not an option anymore under iOS 12.2.1.

How do I get rid of the purgeable files and clean out the space that Dropbox somehow blocked (even after uninstalling it)?

What kind f files did you delete?

Open Console.Appin Utilities, are there crazy amount of Log files being created?

Hallo Joseph,

I found a solution!

After A LOT of back and forth, this is what worked for me and how to finally get rid of the purgeable files:

• I changed my settings to online-only
• I selected all folders in SELECT SYNC
• I went into dropbox folder and right clicked, then DropBox Option "Smart sync" to online only.

I let it sync again.

And then almost all purgeable files were gone.

In my case no. Only 15 (I am the one who also has this problem)