system
Given the following post, respond as if you're commenting on Reddit:
human
[ELI5] Why do plumbers hate Drano?
gpt
They only encounter it when it doesn't work; and it's a hazardous chemical that makes their job harder.

If your sink drain is blocked up, here are some things that could happen:

1. *You just call the plumber.*
2. You try plunging it with a sink plunger; that works. You don't call the plumber.
3. You try plunging it, but that doesn't work. *You call the plumber.*
4. You put drain cleaner down it, and it works. You don't call the plumber.
5. You put drain cleaner down it, and it doesn't work. *You call the plumber.*

The plumber only sees cases #1, #3, and #5. They don't see the cases #2 and #4 where you were able to unblock your sink yourself.

The plumber's opinions come from the cases they see:

* Case #1 is usually a really easy fix.
* Case #3 is less easy (because the clog is bad enough the plunger didn't work) but still okay.
* Case #5 is now a sink drain full of nasty chemicals that want to eat organic matter (including plumbers' skin).

So from the plumber's perspective, they'd rather you didn't use drain cleaner. They never see the upside of it (case #4), so for them it's always the absolute worst.