In message , at 14:12:47 on Thu, 29 Oct 2020,
Roland Perry remarked:
Struggling to find the keywords to guide me to buy online those
plumbing gadgets which clamp on the outside of, and pierce through,
existing pipework to attach a dishwasher feed or something similar.

Thanks for all the comments. Although it wasn't what I was originally
asking for, I've subsequently found (the more expensive):

https://www.screwfix.com/p/self-cutting-drain-cock-type-a-15mm/9543r

Reviews a bit mixed, to say the least.

However, that was after I'd bought and used the dishwasher tap to do a
one-off emptying, and fitted a conventional drain cock.

So I now have a spare dishwasher tap; maybe it'll come in handy if I
feel the urge to fit more drain cocks in the future.
--
Roland Perry