Rainwater tank design for retrofitting

Thanks SaveH20, excellent detail as always!
I shall check out those alarm bell triggers and other queries you mentioned.
Once again, thank you so much for your time and help, much appreciated and we've learned a lot.

hi trixee
I"ve enjoyed this thread and also appreciate the input of H2O!!
Can you please provide an update on the performance of your Greyflow system? Our plans (based on passive solar principles) go to council in Adelaide at the start of next week. All feedback on how our our proposed product has performed for you is most welcome. Neighbours next door have a greyflow and have had some issues with the flush timing and the controller (but hes an engineer who has and i quote "got $50 of bits ordered from the internet and corrected for that")
i guess my question is - are you happy with spending the money (its ~$4k here) on the whole system or would you just add more rain collecting tanks if you had the space?