PVC flexible to regular adapter

The model dimensions fit 20 mm diameter pipes, for both flexible and regular parts.  The funnel-like shape is meant to ensure the drops have as little area as possible where they can stay. The flexible pipe can be screwed on the input end, while the regular pipe can be inserted on the other. Many 3D printing materials are quite smooth and a layer of PTFE, or similar tape, is required to ensure a firm grip on the end inserted in the receiving pipe.

No supports are required, the thread and the funnel have small angles. I have printed it orienting the model upside down on the plate, but it can probably be printed as well keeping the model as in the STL. 

The area touching the bed is small, on both ends, brim or glue or both are suggested to ensure a perfect print.

The pictures show a model printed with transparent PETG, by Overture, extruded at 235 C.