Drinking that much fluid you will get a negetive dillute for sure.
The "excuse" won't work unless they can call a doctor that will give them a medical reason why you are drinking so much fluid.

Sitting in the sauna will do no good. But it feels good anyway.

Detox kits don't work. Its all the fluids they have you take with the kit that may help you pass.

Decide whether you want to sub or try dillution.If you want to dillute read the dillute sticky.If you want to sub,which is what I highly recommend in your particular case, pick up some synthetic urine and practice.