Tidus will indeed find Thanatos at the sinks in the kitchen. (What else is he going to do with a tray of empty cocoa mugs and plates with crumbs on them?) The dirty dishes are stacked to one side, and he meticulously cleans each item one at a time until they are spotless.

"I am doing what I can to support the passengers needing to recover from the mission, and Della cares for many. The fewer tasks they have to worry about the better."