Ha ha! This is a question that someone has filled into a search engine and was directed to eurovelo5.com . Not that they would find an answer here as it is a question I was asking myself only earlier this week as I was preparing for my cycle to work. Doing my own search (which doesn’t list this site on the first two pages of results btw), I note that there is a discussion forum on CTC which in turn directs you to this page on the Ortlieb website itself which reveals that I am doing it completely wrong; I should be “rolling and snapping”. I don’t have my back panniers with me here at home as they are with the bike at work (I was in Oxford yesterday afternoon – long story…). I had been doing it completely differently and cursing the presence of the black bits that clip together!