First of all, let's see how easy it was in Radiant1.4.
1) Create the cylinder and click "thicken":
2) Enter the thickness in units:
3)
You could create the cap manually in 1.5 using a simple patch brush:
1) Create the cylinders, inner and outer:
2) Create a brush and click curve>simple patch mesh
3) With the new patch mesh selected press "v" and position the vertices like so:
4) Duplicate the new brush three more times and rotate into place, use shift+s to align the texture:
Since a player is expected to interact with this pipe, I wouldn't suggest using patch meshes, their collision detection works pretty bad.
Instead you could use them as a blueprint on which to place the regular brushes on, much more reliable:
Remove the patch brush, duplicate and rotate the brushwork further to get the needed shape
