[Delphinus]

I think it depends on the grade of kalk you use though. I've had stuff that discoloured to grey after a week or two and others that would turn yellow and wouldn't dissolve any further. For that stuff it may be handy to have a drain valve, maybe a little John Guest style thing tapped into the bottom would work nicely.

Only thing is I would rinse my whole reactor out with vinegar every time I cleaned mine out so I was basically taking the whole thing apart anyhow.

But I don't see any downside other than potential clogging which could be cleared up easily anyhow.