Down by the river

8/16
I went into each chapter and flushed the all toilets then got "Down by the river" achievement.

#1.Not sure it is the number of toilet flushes that dictates achievement.
Chapter 9 has five toilets, and I've flushed them over 50 times and still can't reach the achievement
Chapter 10 has four toilets, I flushed them many times and still couldn't reach the achievement.

#2. You can just go back to the chapter and flush the toilet , then abandon the mission and it still counts.

So I think the most certain way to get this achievement is to flush all toilets in each chapter

[YukoValis]

I believe it is number of toilets. I've seen people get this achievement before even unlocking the last level.

[AmeliaNikhol]

Flush AT LEAST one toilet in each level, AND the toilet in your own apartment. The apartment toilet was the only one I missed and as soon as I flushed it, the achievement popped.

[tsengar]

I believe that the achievement is to flush every TYPE of toilet. I could be wrong, but that corresponds with my experience and the things I've seen people report to not be triggers for it.

[Nyu]

i for sure didnt flush EVERY toilet in all levels
but i flushed atleast on toilet in all levels including the homebase and i got it.