Thanks for the replies everyone, it's much appreciated though it feels as though we've strayed onto the topic of whether or not we should worry about oxygen during dry-hopping, whereas I've already decided that yes, I do worry, and I'm going to take some reasonable steps to reduce it as much as I can. Those PET sample tubes mentioned by @Buffers brewery are going to be my starting point and I think I've found some that may work, but I'll need to confirm that they have a compatible PCO thread for my ball valve. If that doesn't work out I'll investigate the tri-clamp lid suggested by @Davegase but as others have said this will increase the height of the fermenter to the point where it may no longer fit into the fridge. By the way @Davegase - do you have a link for that thing? Can't seem to find it on any UK retailer's site.
I've heard of this approach before and like its simplicity, but I do wonder how much of the goodness is lost by flushing the hops with CO2 during the fermentation process. Must smell lovely in that fridge though!
Now I fix my dry hopper under the bucket lid, fill with dry hops, close and fit to the bucket after pitching the yeast. Once the bucket is in the fridge it stays there until it’s empty (after transfer). The dry hops are added by simply moving a couple of magnets on the lid, takes literally a second.
I've heard of this approach before and like its simplicity, but I do wonder how much of the goodness is lost by flushing the hops with CO2 during the fermentation process. Must smell lovely in that fridge though!