Thunar respects the specification when deletes files from other than $HOME partition and creates the $topmost/.Trash-$UID directory and moves files to it. But Trash listing do not includes these trashes from not $HOME partition and do not delete them while Empty trash action. The specification tells: "When preparing a list of all trashed files (i.e. to show to the user), an implementation also MUST check for .Trash in all top directories that are known to it."
There is an ongoing debate on gnome bugzilla https://bugzilla.gnome.org/show_bug.cgi?id=604015 if this is a bug of the gvfs backend or nautilus. We should monitor this closely, because if they decide to fix it in nautilus, thunar will need its own adaption to handle trash locations cleanly.
*** Bug 10163 has been marked as a duplicate of this bug. ***
*** Bug 10006 has been marked as a duplicate of this bug. ***
New upstream bug: https://gitlab.gnome.org/GNOME/glib/-/issues/251 Changes were made to glib/gvfs, I've just tested with a flash drive all seems to be working as expected. (Thanks b3nmore for the link).