Household central ducted vacuum cleaner system short flanged elbow for use with the switched flap valves.
These elbows are usually fitted to flap valves, where they come down the wall cavity, a wall plate can be screwed to them, which will alow the flap valve to be secored to the wall in a plasterboard wall. The ducted vacuum PVC pipe fits in the non flanged inlet in the back.
Incidentally, short elbows are fitted in this position, so they jam items like pens here at the flap valve outlets where they can be easily be removed because the bend is too small for long objects to get around.
As it's light, maximise the saving on postage and buy some of the related parts below, such as dustbags and the filters or a new floor tool.
At the moment, standard postage within Australia is capped at a maximum of $20!