what was in the drain you need to talk to kevin

The most likely answer is that it was drain cleaner that got into Celia’s eye, and the “Kevin” reference points to We Need to Talk About Kevin. In the story, Eva finds drain cleaner left out, and Celia later says Kevin helped wash it out.

What happened

• Celia is injured when drain cleaner gets into her eye.

• Franklin blames Eva for leaving it out, while Eva blames Kevin for not watching Celia.

• The scene becomes a major point of tension between Eva and Franklin.

Why this matters

The “drain” clue is a shorthand for that chapter’s bathroom incident, not a separate mystery object. The key detail is that the substance was drain cleaner , and Kevin was involved in the aftermath.

Tiny context

The chapter summary also notes Celia later says, “Kevin helped me wash it out,” which is why Kevin gets pulled into the incident.

TL;DR: It was drain cleaner, and Kevin helped wash it out afterward.