laakkone wrote:
@CamBen: You shoud make those brush based pipe 90 degree turns more smooth. Now it looks like you've just clipped them in 45 degree angle. You can do this with torus brush tool.

Basically I tried to do this, but in every case, after creating a torus and saving/reopening my map, they are all counted as invalid and removed immediately. Is there any workaround for creating curved cylinders?

You could make a 360 degrees arch (remember to make them always 360 degrees and then cut) but a bit extended at its edges so it looks like a cylinder, then use the clipping tool to cut the arch shape (corner) you need to connect 2 pipes, and the vertex tool to join the vertices and fit the corner to the pipes (remember to make the arch and the pipes the same number of sides... use at least 24 or 28 sides )