Pete, I share your frustration re different hose & coupler diameters. All my portable power tools (e.g. jigsaws, sanders, routers, etc) and all my bench top machines (e.g. bandsaw, disc sander) ALL have different diameter extractor ports, and just as you say, it's a real faff cobbling up bits and bobs with gaffer tape to get hoses to fit. To add to that, the extractor ports built into the disc sander don't do much in the way of extraction anyway, even after I have fiddled & faddled to get a hose attached.
A bright(er) spot - I don't know how it is in UK these days, but here shops which sell stuff like vacuum cleaners (domestic) have to take busted ones back for disposal. Our local supermarket has a big box full of such "carp" in the carpark and I've found several discarded vac hoses which, much to SWIMBO's disgust, I've collared. One was a direct fit onto the extractor port of the bandsaw and works well with the cheapo Lidl ashes vac (the other hose end fitted directly into that vac) but in general they're all (slightly) different sizes so it's all more than a bit of a hassle! (BTW, I keep looking for a discarded Dyson so that I can pinch the cyclone bit to save making one - or a Thein - but so far no luck).
As said in an earlier post, my shop is in the cellar, a big advantage in several ways, but as it's shared with " 'er upstairs", for stuff like the central heating boiler and the washing machine & tumble drier I am also under some pressure to radically improve dust collection and reduce noise. Hence my interest in this thread (it's not only jealousy). So thanks for posting.
Cheers
AES