I have also found I have to twist the little plugs- and I also have to pull them out and poke the little holes with a twig to remove any wax or propolis the bees leave. Otherwise the channels can be up to halk full of honey after I have robbed a frame.
Also I noticed that on my last robbing the honey was not 100% crystal clear liek the first time the frames were robbed. It was 99% clear- with just the odd speck of dust.
It does bother me a little bit- not so much from a health perspective- but I just liked that there pretty much zero need to strain Flow honey. I am now thinking I might get a bottle brush and work out a syphon/pump system to periodically wash out those channels. If you poke your finger in there it is nice and warm- all the time
Does anyone think a small amount of water dripping over the brood frames would cause much of a concern? The channel is made up of segments with small gaps in-between and I am thinking if you flush water through them a very small amount will end up dripping through the brood box. If I was to do it I would only do it on warmer and drier days.