I have a system that has been working perfectly for 4 years. Just last month, though, we starting noticing puddles of water in the worm bed at times. Since then, the drainage is very slow, and although the water drains, it's SLOW and backs up in the tank.
I have since flushed the pipes, thinking maybe they got blocked, but they were not blocked at all. The water still comes out clear in the drain field, it's just a trickle, though.
It seems like the restriction is the worm bedding itself.
Do we need to remove all the old compost in there and add new material, now? We periodically top it up with coarse wood chips, and we just add to keep it topped up, but maybe there's some sort of worm poop layer somewhere that's restricting flow?
Not sure what to do, but we have loved this system up until now. If we could figure something out without having to remove all the compost, that would be good.
I'd advise just gently forking through the material in the tank. Without seeing it, it's impossible to diagnose precisely, but material settles as it decomposes and becomes more dense. Introducing more air by lifting the matieral should help drainage. Try that, see how it goes, and if it becomes apparent the slow drainage is further down, then a deeper intervention may be needed.