This is an adapter for a 4" port on a dust collector to two 2" shop vac hoses. I have a router table that has an upper and lower dust collector port, and needed a way to connected them both to the dust collector.
This was printed in ABS and glued with epoxy, and didn't collapse even after connecting the two 2" ports together.
The 'wall' variable in the OpenSCAD file allows setting the thickness of the item.The 2.96mm value is recommended by Slic3R PE when setting the perimeters to 4 and checking the 'Detect thin walls' option.
The 'port_small' and 'port_large' array are just for reference. The actual values are hard-coded within the source. The top and bottom half are connected with a small cube so that the part is manifold and can be printed in one session.
In Slic3r PE, set Layers and perimeters->Vertical shells->Perimeters to 4, and check 'Extra perimeters if needed', 'Ensure vertical shell thickness', 'Detect thin walls', and 'Detect bridging perimeters' (the last one probably isn't needed, but it's always checked)