How to easily find leaks?

Tiftid

the Embodiment of Scarlet Devil
aa
Sep 10, 2016
531
398
Go to File > Load Pointfile:
1700065262848.png

This will draw a red line throughout your map; following that line will eventually lead you to a "hole" in your map which exposes it to the infinite void beyond.
To fix the leak, you must seal it with a world brush (one created through the brush tool and not turned into an entity, not even func_detail).
 

Yo Yo Bobby Joe

L1: Registered
Nov 9, 2021
34
4
Like the person above said, you'll want to hit load pointfile. One thing to note, however, is each compile generates only one pointfile. So, if you have more than one leak caused by different problems, you'll need to compile multiple times to regenerate the pointfile until all entities stop leaking.