entity trigger_multiple (-3854.14 10497.00 -895.88) leaked!, and it changes every time. I deleted what it tells me is leaking, but it always finds something else to leak.
Water is a special texture that changes the whole brush into the "water" volume, which doesn't seal, even if nodraw is on the other faces. Just add a nodraw brush underneath it.
Certain textures convert a brushes properties. A lot of tool textures will do this. Glass textures will do this, basically any texture with alpha transparency will do this. The brush is converted from world geometry into... not world geometry.
It does, but it also needs to be a "world brush". This means that it cannot be tied to an entity, or have water on any facing, or turned into a displacement, and there's probably a few other exceptions as well. However, if you just make a brush of any size and give it (almost) any texture on every side, it counts as a world brush and will seal the map. Nodraw is a useful texture to use for this because it does not get rendered in game, which means that it makes your map easier for computers to process in game. Some good examples of nodraw usage are to seal off water at the bottom of a map (like you need to do!) or to seal off the bottom of the map when you have displacements as ground.
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