Thanks for all the tips. It seems I have started at the same time as Tazio. I developed my first two films yesterday, HP5 120 film and Delta 3200 120 film. It was much easier than I thought it would be, and less smelly. And the negs came out well, too.
I didn't realise that you could just twist the paterson loader though. I'll do that next time. I was just pushing it in!