It was only $100 or so more than a 15,000l tank and I thought that was good economy, but in retrospect, I’d rather have the 15,000 jobbie. 22,500 one is too tall.
Installation added a few grand though, because I needed a small jobbie (1,500l) to collect the water, and then pump it to the big unit in the back corner of the property. So the pump, the extra tank and the pipes added a good 3 or 4 large.