Caulk..
Caulk is an invisible texture when compiled. If you were to make a map of completely caulk it would be the smallest filesize ever, thats because when you compile, the compiler ignores it.
If the player cannot see the texture when walking around, then the texture should be caulk, this will save on loading time, make the fps higher, compile time will be shorter, filesize will be smaller.
So here is a quick tutorial on
Using caulk (and the "Side manipulation tool" and "clipper tool")
1. Select the common texture from the textures list.
2. Find and select the caulk texture
3. Create a large selection in the top view using your mouse
4. Hold CTRL + Shift and select a side to texture (the side must be visible ingame
5. Select your texture
6. Make a wall in the side view
7. Press E to bring up the side manipulation tool (Blue dots should appear around your brush)
8. Make a miter joint by dragging the inside bluedot downwards
9. Do it on both corners of the wall
10. Do the same for all 3 other walls and a roof
11. Select the sides using CTRL + Shift, then texture
12. The inside of the box we made still has a floor, we need to remove it.
13. Select the floor using Shift + click
14. Press X or select the Clipper tool, then select 2 points on the brush to cut along the line
15. Cut all the way around and finally delete the inside floor
