A trapdoor can be pulled down from the ceiling.
|When the trapdoor is pulled down, thick sludge pours down onto the victim.
A DC 16 Wisdom (Perception) check reveals a bit of moisture around the edges of the trapdoor.
A DC 16 Intelligence (Investigation) check shows the moisture to be raw sewage.
When the trap door is pulled open, a container of sewage tips over and pours down the door. The target must make a DC 14 Dexterity saving throw or be covered in sludge. Every hour that the target is covered in sludge they must check to see if they are infected with sewer plague.
Also, while covered in sludge, any social checks are made at disadvantage.
It requires 1d4+2 round to clean off the sludge and also requires 2 gallons of water. 1 quart of water can be used if clothing/armor is changed.
The trap can be disabled by either remotely pulling down the door by fashioning a device, or by pushing up on the trap door and letting the bucket slide off the door. The latter requires a DC 14 Dexterity check. If this check fails by more than 5, the door opens and splashes the sludge onto the target.