Rainwater tanks in BAL FZ

Hello, I am after some guidance on installing a rainwater tank in BAL FZ. I know that I need a metal tank. However my supplier has told me that to install a wet system my metal downpipes need to be partially replaced with PVC so that they can hold water.
Am I allowed to use PVC in BAL FZ? I have tried to interpret AS 3959 but I am unsure.
If I can’t use PVC is there any other way to install the tank with a wet charged system, or do I need to change the design so that it is excavated in and gravity fed?
Note I need to obtain a CC so can’t go ahead and install without a PCA reviewing.
Any advice would be appreciated, thanks

doesnt matter what the charged system pipes are if they fill into the top of the tank
the outlet pipe must be metal
and i would assume if you are filling into the bottom of the tank, then this pipe would need to be metal

All BAL's are not interested in the material used for downpipes.
You wont be able to do a charged system unless you use pvc, the solvent cement glue provides a water tight connection.
The Inlet to the water tank is at the top of the tank, not at the base otherwise you would need a gate valve to be able to shut it off if you developed a leak.
The tanks inlet is lower that the downpipe connection at the gutter nozzle.
The outlet from the tank must be a special type of connection (subject to which state you're in) to allow for your's and the fire service hoses to simply connect on rather than having to put different bushes on to accommodate the hose.
The issue is if there is a fire, it will melt the downpipes, but it's not as if the downpipes will be needed in a fire??
The downpipes are ultimately sacrificial.

Hope this helps

Thank you it really does, appreciate your response!