Graeme wrote:
In message , Dave W
writes
On Tue, 11 Jun 2019 11:10:05 +0100, Graeme
wrote:

Put through the dishwasher last night, which softened the crud,
and currently sitting in a cup of hot water with a dash of washing
powder.

Now you've softened it, perhaps a bit of added pressure or suction
might help, e.g. hypodermic needle?

Job done! I think sitting in hot soapy water softened it, and a
combination of guitar string, contact cleaner and a can of compressed
air finished the job. Delighted :-)

Had a similar problem many years ago. I used to top up the washer bottle
from a kettle. The kettle needed descaling and bits of sediments were being
introduced into the washer bottle.
Lesson learnt.