Is it worthwhile every few months putting some Caustic soda crystals
down the toilet to prevent blocking?

Every year my toilet gets blocked. About half an hour with flexible
rods and "pumping" with a toilet brush seems to push it all through.

I live alone so I know what goes down there - and there ain't nothing
that should cause a problem. However, the soil pipe has all kinds of
interesting bends and twists into a shared soil pipe for all the flats.
Now the problem doesn't occur in the shared stack (though it would be a
nightmare if the shared stack did block as there are no "inspection" or
"rodding" points along the pipe - and the bloody thing is inside the
building. God help us if it blocks.)

So, I am guessing the rather twisted nature of the pipe from the pan
makes it vulnerable to blocking. Can I keep it ultra clean with
chemicals or will it just block from time to time?

Thanks

Clive