It's hard to say from here tbh I would have to see it,most plumbers/builders merchants would sell a kit for a few euro with both washers in it,when putting it back together you may have just pinched a washer and that's enough to cause a leak,sounds simple but it can be that easy. Hope this helps.
Woman in shop said I just need the black rubbers (ooh err missus). Going to try now, will report back in a couple of days.
You won't be able to see the tiny ridge in my huge pics. If you look at my previous picture or my first picture, the end with the dirty creamy connecter thingy doesn't seem to stay attached to the nut.
AND WTF HAS THIS SITE BECOME WHEN WE ARE FOUR PAGES INTO THIS AND NO ONE HAD SAID THIS THREAD IS PLUMBING NEW DEPTHS. YOOZ DRIVE ME ROUND THE U BEND.
If it was Patience who knackered the plumbing in the first place you should make her capture all the sink waste in a bucket and get her to throw it out at the same time she clears the bucket of her poo poo.