Help with Seaman's Penis Vacuum Pump sleeve

Hi folks I recived this penis pump yesterday http://www.lovehoney.co.uk/product.cfm?p=1733 and got straight into giving it a go. After cleaning I had a bit of bother getting the sleeve back into the pump itself can anyone give me advice on getting the sleeve back into the pump a bit easier? I found I could get the sleeve up so far then it wouldn't budge any further. Thanks