On Fri, 15 Jun 2018 12:28:22 +0100, T i m wrote:

snip

Now, I could unscrew the waste outlet itself but it's been there since
I fitted it all 20 years ago so I would rather not so are their any
100% 'chemical' processes (enzyme cleaners .. vinegar and baking
powder?) I could try or is it inevitable I will have to strip it down
and clean it out mechanically? ;-(

Anyone know if they do a blanking cap to fit a std basic waste (1
1/4" is it)?

If they did I could remove the trap, fit the blanking cap, open the
plug then fill the basin to the brim with whatever cleaner is best and
leave it like that overnight. That way it should clean the inside of
waste and the overflow circuit?

Cheers, T i m