Paper2002AD wrote:

I have a blocked toilet - the bowl drains very slowly, suggesting a 90 - 95%
blockage.

Pumping up and down repeatedly with a large plunger has made a big improvement
- estimated blockage now down to 10%

How to clear it completely?

Tip caustic soda crystals fllowed by kettle of hot water, down it,
wearing usual safety nanny googles and gloves, and cover with a plastic
bin liner till it stops fizzing.

Then leave for an hour or two, then flush.

If you suspect heavy pipe scaling pour a half gallon of brick acid down
it and wait a day till it stops fizzing.