Re-Use a Time Machine backup disk.

This is more of suggestion than a question - how to save yourself a bunch of time.

Having just upgraded my OS and got everything working (long story) - I wanted to establish a new, clean, Time Machine Backup - for this operating system (Sierra). I made the fatal mistake of trying to use an old Time Machine disk by deleting the backup files. It has taken about half a day to select 9 million files for Trashing, and is now going to take many more hours actually Emptying the Trash.

I am pretty sure that I could have gone into Disk Utility, re-initialised the disk in a couple of minutes, and been up and running the new TimeMachine Backup.

Complete waste of a day !!

Be warned !! (but perhaps you all knew it)