Interesting tip if your Aeropress is slipping, to expand the plunger's rubber while contracting the tube. Maybe I'm just not an adequate Aeropress user, but mine shows no slippage at all. And I'm almost through my third pack of filter papers.
On second thoughts, maybe the reason my Aeropress plunger has never slipped is that I brew upside down. So the water is heating the rubber while the grounds are brewing. And the rubber expands more than the plastic of the cylinder.