A waste disposal unit was a device used for the disposal of various waste products.
In Paradise Towers, Tilda and Tabby had a waste disposal unit in their flat. After they had kidnapped Melanie Bush, she pointed out that something was wrong with the device and as Tabby went to inspect it, a cleaner's claw emerged from it and dragged her through.
Tilda blamed Mel for the incident and went to kill her, but was interrupted when Pex broke in. As she went to fetch a knife, the cleaner broke through the unit again and dragged her through. Both of them were killed. (TV: Paradise Towers)