Immersion Tank - Plumber help please

Fitting new cylinder
The sides have 28mm male threads and a sticker on the side "do not use tapered fittings"
Next to all the tanks in B&Q are a load of tapered fittings
so what type of fitting do I use to bring it down to 22mm ?
I've seen a simple flat ended 28mm reducer to 22mm that will do the job but with no olive, will the cylinder be happy with lots of PTFE tape on the thread ?
Now: YZF-R1 (for sale)
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