Yeah I’ve pushed many a chimney liner down stacks 
it’s no easy task standing on top of a chimney spinning the tubes to get them around bends like a massive lasso to get them down a chimney. It may only be 10 - 15 meters from pot to ground level vertically but how stacks are built you can add an extra 5 meters on as they run on angles through a house with several bends before you hit ground level.
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