Have always swept from the top down, section of plywood to fit hearth opening and tape up with masking tape, prop grate against it at an angle, (just in case)
Up on the roof and sit on the stack and rods and brush down and back up twice, turning clockwise.
Many Years ago when I was serving my time with an old chap from Caithness he told me that when he was a "loon" and stayed up a glen between Helmsdale and Lybster he used to lend a hand to the estates he worked on. (would have been in the late 1940s)
Anyway this day he was dispatched to Dunbeath Castle with an old chap who was going to sweep a chimney.
They arrived at the castle and were shown to the room that had the chimney needing swept. The old chap said in a broad Caithness accent, "will ye go out there loon and gie me a shout when the brush comes oot the lum and come in here to let me know"
Out he goes and up the bank at the back of the castle sitting there for a good few minutes and gazing up at the cans on the roof. A few more minutes passed and still nothing and the old chap appears shouting "anything there yet loon?" "No" he replied.
The old chap disappeared again and he continued watching for another while.
The old chap comes out again and up the bank thinking he was not seeing the brush or taking the mickey and half expecting to see a brush and rods sticking yards out the top.
Still nothing. "Ok I'll try a few more rods but it is hard going" Away he goes and another 10 minutes passed and he was out again.
Still nothing to be seen. Lots of head scratching and the old chap said, we'd better go inside for a look.
Off they went inside and ended up in a room a couple of floors above the room the old chap was sweeping.
By this time in the story the old chap I served my time with was near bent over double in hysterics




He recovered after a bit and said that the brush and rods had pushed a grill/hatch off the wall in the room 2 floors up and he (with arms waving about, this way and that) was describing how the brush and rods had left very little of the room unscathed.
The room had some historical significance apparently as some dignitary had stayed there in the past


I still have a laugh if I am down by the harbour in Dunbeath looking across to the castle.
Cheers