Empyting the Trash where I dumped an entire unwanted Time Machine backup -- keep getting messages I cant because "the item is in use"

Sorry for yet another Q....

I have two external drives with Time Machine (TM) backups. The older, 2 TB drive has two volumes on it, one with a ~5 year old Time Machine backup (that stopped working and no longer need it) and also a few VIP docs in folders. Other volume had bootable OS.

Now I really need that 1 TB + of hard drive space. So I dragged Time Machine back-up to trash. I've been trying to empty the trash for almost 8 hours! And I'm only halfway through. Worst of all I keep getting error messages that "operation can't be completed because XXX is in use". Strangely these come in rapid succession, always starting with an old file/app "Quicken copy", then up the directory ladder to "Documents", my User "Name" folder, "Users", "Macintosh HD is in use", and then what looks like a Time Machine backup name with "Year-Month-Day-numeric" file name. I click "Continue" every time and I get the same string of messages over and over. I keep having to click "Continue" every few seconds.

What to try next? Could Time Machine (which is turned off) somehow be "talking" to a relict back-up? Why would my OS care what is on that drive when docs/apps on it are open? Should I restart? If I disconnect the drive, but haven't emptied trash wont trash still be there?

Saw this article on MacWorld about deleting stubborn items in the trash but it seems more relevant to internal, boot drive. Why would Start Up items have anything to do with Time Machine?

https://www.macworld.com/article/232436/how-to-delete-a-file-that-macos-says-is-in-use.html

I cant just erase whole volume because I have other important folders on it. And no space to copy those to. This drive wasn't used much so I think its basically healthy.

TIA....