axley

I'm pretty sure it's the collector above a sink or other things and the surrounding tiles including diagonals so it should be able to use 9 in total (I havnt tested this yet, but I saw this on a tutorial video) edit: also in case you didn't know you have to use a pipe wrench to plumb

The idea is that currently, you can only place 9 rain collectors for each item such as a sink. I suggest that you can add more rain collectors and require adjacent collectors have a hole on the side that faces the other collectors to allow more water to be drained from all the collectors. Visual example: