Drain

Examine: This drainpipe runs from the kitchen to the sewers

Drain is a piece of wall scenery located in Varrock and Sinclair Mansion. It connects the kitchen sink to sewers. In case of Varrock, it goes to Varrock sewers.

During Demon Slayer quest, a bucket of water is used on the drain in Varrock in order to wash down silverlight key 3 and collect from the sewers.

Location of Varrock Palace drain

Murder Mystery drain

During the Murder Mystery quest, the drain in Sinclair Mansion must be investigated under the guards supervision if Carol Sinclair is suspected guilty or the player hasn't been able to determine between the six members of the family.

Investigating it prior the start of the quest and after its completion:

You need the guards permission to do that

Investigating it after accepting the quest:

Its the drains from the kitchen

Investigating it after the player has spoken with the Poison Salesman and the distinct family members leads to two cases. One in which Carol used the poison on the drain (not guilty) and one in which she didn't (guilty).

Investigating when Carol is not guilty:

The drain seems to have been recently cleaned

You can still smell the faint aroma of poison

Investigating when Carol is guilty:

The drain is totally blocked

It really stinks. No, it *Really* smells bad.

Its certainly clear nobodies cleaned it recently.