Please note that Trash It 6.x and OS X 10.11 FINAL release are compatible. It has been tested with El Capitan (10.11 Final) and no issues were detected.
An incremental upgrade will be released shortly that makes better use of El Capitan features, but in the meantime, there should be no problems. Please use our contact form to send any issues you run into while running El Capitan (10.11) and Trash It. Thank you.