Weapon_portalgun inside map leaks
In my upcoming map, Wheatley's Punishment 02, My weapon_portalgun leaked, although it was inside the map! How do I fix this?
1. I guess you already know how to find leaks, but just in cases: once your compile tells you there's a leak in your map, go to Map > Load Pointfile. This will draw a red line from outside your map through the leak and will reach the portalgun: a leak can be either a little hollow between two brushes or maybe it's a func_brush or func_detail or whatever other entity, which don't seal a map.
2. Sometimes, stuff into the map have their center of origin outside the map. Go to Tools > Center Origins
3. Some other times you can have an annoying (and useless I think) option/feature enabled which is called Radius Culling and looks like this: 
Check out and if it's enabled, just disable it 
useful tools and stuff here on TWP 
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Also, just because the pointfile line is pointing to that particular entity, does NOT always mean that it is that entity which is causing the leak. There could be a hole in a wall and that particular entity is the first entity that the compiler found. You should follow the pointfile line to see exactly where it comes into the map.
PortalStories.com
"Oh, in case you got covered in that repulsion gel, here's some advice the lab boys gave me: DO NOT get covered in the repulsion gel."
Turns out I had multiple leaks that are so tiny they are almost invisible.
Sounds like you're not working on grid or on a very small grid.
My recommendation is use a size 16 or 32 grid and have snap to grid on.
This way your brushes will get proper sizes! It will make leaks a lot less frequent and it'll also make them a lot easier to spot!
Sounds like you're not working on grid or on a very small grid.
My recommendation is use a size 16 or 32 grid and have snap to grid on.
This way your brushes will get proper sizes! It will make leaks a lot less frequent and it'll also make them a lot easier to spot!
Even if your map is overly complex and has indents everywhere and aligns someplaces to 1 unit - always make the main layout snapped to a large grid first!