Push about half of the leading flexi rod up the flue.
Allow enough exposed rod so you can comfortably bend it to line up the next rod.
You should find most of the loose soot will fall inside the pipe. Or you could tape a damp rag around the pipe just above the hole, to contain any excess dust.
Continue to attach further rods as you proceed up the flue.
Each flexi rod will spin on easily if lined up straight.
Use the latex coated gloves to grip the rods. Never use excessive force, hand tight only.
Both ends of every flexi rod have been connected to another rod to make sure all the threads mate easily. The Brush adaptor threads are tested too.
If (due to their newness) you find some rods slightly more resistant to twist together, use a tiny bit of soap or washing up liquid on the thread to lubricate it. Wipe threads clean after the first use, as nylon is self lubricating and wont be needed again.