You can thank the user testingresults over on the Kali forums for this one. That link will take you to his guide, which is much better than what I have.

Very quick reproduction of the guide follows.

apt-get install scrub
vim empty_trash.sh

#!/bin/bash

find ~/.local/share/Trash/files ~/.local/share/Trash/info -type f -print0 | xargs -0 -I{} /usr/bin/scrub -Sfp random {}

find ~/.local/share/Trash/files/* ~/.local/share/Trash/info/* -depth | while read i
do
    cleant=$(head -c17 /dev/urandom | tr -d [[:space:]] | tr -d [[:punct:]])
    mv "$i" ~/.local/share/Trash/files/"$cleant" 2> /dev/null
done

rm -rf ~/.local/share/Trash/files/*

chmod +x empty_trash.sh

Then run it whenever you need to empty the trash.