Ahhh I see, that makes sense, then, id only seen klargester in connection with the treatment plants. For the main house we had one built old fashioned style out of blockwork,so I was thinking we would do the same with the cottage, but tbh that was just an assumption so I might be wrong!
No demolition here, just restoring and extending cottage (house is grade B listed so I don't think they would take too kindly :-DDD)