Fitting for a rain gutter downpipe

A downpipe fitting for coupling between a top and a bottom of a rain gutter downpipe, said downpipe fitting comprising:

• a first part having an inlet at one end, an opposed other end, and a longitudinal extent therein between, said inlet being sized and shaped to couple with a first section of said downpipe above said downpipe fitting;
• a second part having an outlet at one end, an opposed other end, and a longitudinal extent therein between, said outlet being sized and shaped to couple with a second section of said downpipe below said downpipe fitting;
• a rotatable joint joining the opposed other end of said first part to the opposed other end of said second part, said rotatable joint comprising one of an annular ridge and an annular groove on one of said opposed other ends, and the other of said annular ridge and said annular groove on the opposed other one of said other ends;
• and
• a flow path for rainwater through said downpipe fitting from said inlet to said outlet via said rotatable joint;
• wherein said first part and said second part are configured to rotate about a substantially straight longitudinal axis defined by the longitudinal extents of said first and second parts and downpipe fitting,
• wherein rotation of said second section of said down pipe about the substantially straight longitudinal axis is decoupled from said first section of said downpipe by said rotatable joint, and
• wherein said inlet at said one end of said first part is rectangular or square in cross section,
• wherein said inlet of said first part has an inlet cross-sectional area,
• wherein said rotatable joint is circular in cross section,
• wherein said rotatable joint has a circular cross-sectional area with the circular cross-sectional area of said rotatable joint being smaller than the inlet cross-sectional area of said first part,
• wherein said outlet of said second part is rectangular or square in cross section,
• wherein said outlet of said second part has an outlet cross-sectional area larger than the circular cross-sectional area of said rotatable joint, and
• wherein the downpipe fitting further comprises:
• a first transition portion, that is a tapering rectangular or tapering square shape portion, said first transition portion extending from said first part to said rotatable joint, and
• a second transition portion, that is a tapering rectangular or tapering square shape portion, said second transition portion extending from said second part to said rotatable joint.