The reason we care is that the cylinder contains the rainwater that is used to flush my loos and wash my clothes. Thus I would like to have a rough idea at what depth of water I should set my system to add mains water so that I dont end up leaving a huge floater in the loo.
If you're depositing a huge floater (pre flush), shouldn't you be worrying about your own internal plumbing rather than that of your residence?