Rain water tank/storm water/house leak issue

Hi PC members,

Recently our interstate rental (built in 1950th) experienced water leaking on the boxed gutter flat garage roof and ceiling which need a complete replacement. We have 2 builders (one with plumber) came in having a looks and mentioned that it the cause of the damage could be stormwater overflowing issue that may or may not associated with rainwater tank (20k ltr).

The one with the plumber could not pin-point where the problem is, just say there could be a burst pipe or leak somewhere and the the storm water pipe for the whole house (70m) need to be replaced.
The 2nd builder said the issue was caused by the inflow of the water tank is higher than the gutter the water flows back to the house when the tank's water is full. Suggest to lower the pump innet.

Obviously two very different opinions. I am thinking to get a couple of more plumbers to have a look to find the exact cause? Should it be a plumber who has rainwater tank experience?

Also, does the plumbing need to be fixed before the roof replacement?

Does anyone have any suggestions/experience in this type of issue?

Thanks!
NM

 

Can't comment on the cause but always get the problem fixed before repairing the damage.

 

rainwater tank higher then roof you sure?

 

Not sure and skepitcal about it.

 

I'd suggest a plumber to investigate the box gutter. It's possibly blocked or rusted. You haven't got any photos of the top of the RW tank/inlet, the box gutter or ceiling.