You've run into the (getting infamous) immutable flag problem; run
chflags -R nouchg ~/.Trash
then try your rm again.
I could have missed something here, but with full root "rm -fr /Volume/frakkedHD/.Trashes" should work, but it doesn't.
The chflags was a nice idea, but I still get "Operation not permitted" for thousands of files. GORRAM APPLE!!! :-(
What have they secretly done behind my back THIS time???
It would appear that the ONLY viable solution is to REFORMAT the drive. As this is my backup drive, that's not a very nice thing to require. If my primary HD goes down during the reformat then I've lost 1TB+ of data.
Time Machine is definitely Not Ready For Prime Time. :-(
We need a ROBUST OS, and a ROBUST backup solution, not more crap from Apple. I've been slowly approaching utterly infuriated with Apple for decades now. The last time any of their stuff "just worked" was circa 1984.
Unix *should* have given us the tools to solve OSX insanity, alas, OSX seems to be the master behind the curtain, leaving even full root helpless.