force empty trash?

I have been moving some things around, I had an external drive that had all my work data plus it doubled as a time machine backup for a short while in a transition period. I got a new external drive strictly for time machine which will back up the other external drive as well as my iMac. I did not want a backup on a months worth of time machine backups so I removed it in settings and dropped the time machine backup in the trash. I went to empty, took a long time and deleted most of it but there is still a bunch of time machine backups left and I get messages saying I cannot delete as files are still in use.

How do I force empty the trash? Running OS 10.13.6

via ehMac.ca https://ift.tt/33QiWqA