Asking plumbers here. I am based in VIC

Post covid installation of Bidets / Toilets with bidets has become very restrictive. With multiple VBA guidelines. The requirement of installation of RPZ valve and yearly checks cost is a major turnoff for small residential household. I want to do the right thing and at the same time something that is affordable.

Have a few questions.

1) If we buy toilet that is having built in bidet system, does law says we still need to do RPZ ?

2) From reference 3 below
*A douche outlet installed at least 25mm above the overflow level of the pan, at any position, does not require a backflow
prevention device.*

does this mean when douche outlet can satisfy above, no RPZ value is needed? This seems to be the best option.

3) If RPZ is mandatory in all cases, is it possible to install one small tank outside, manually fill it with fresh water every few weeks and just use that for the toilet bidet? Talking about something like this https://www.oztanks.com.au/products/1000-litre-thin-tank/. That tank will not be connected to mains, so no question of backflow comes up.

See this diagram for example design with two options

Option 1 - Separate drinking water tank used for bidets and is manually filled

Option 2 - Tank automatically filled using ball valve (preferred option)

Paying $2500+ for RPZ install and $300+ for RPZ testing is not an option that I can afford.

References

https://www.vba.vic.gov.au/__data/assets/pdf_file/0005/154481/BP-02-Toilet-seat-douches.pdf
https://www.vba.vic.gov.au/news/news/2020/vba-issues-health-warnings-over-diy-bidets-and-alternative-toileting-devices
https://pureplumbingpros.com.au/plumber/information/toilet-bidets-and-backflow-prevention