I personally stay clean of the flexy waste pipes as over time they can collect muck inside and block up, which is the last thing you want on your shower tray which will have limited acess after installation. If you want to connect 32mil pipe to 40 mil pipe then you can buy reducers from any DIY shed or plumb centre. This will fit your 40mil and reduce down to 32mil. Hope this helps. Good luck mate.
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