Sounds far better than the cost weight etc of an extra water tank just to have the extra available on odd occasions.
I'm just a bit wary of the potential piercing of the bladder on rough roads...but time will tell and I'd be interested to hear how it goes.
Just as a comparison (and everyone is different) we fill our two tanks before going bush...160 litres....add two 25 litre portable bottles (Jerry can size) and a slab or two of Coles or Costco water bottles for drinking.
We can get two good showers from the 22l heated, toilet flush tank is 20 litres and lasts about 3/5 days, washing up etc takes about half to one litre at a time.
So that gives us our 10 days .....and, as it always rains when we go away, we supplement that with harvested water from the awning. Last trip was 10 days bush and we came back with tanks over half full...and, yes, it did rain.
I think we'd still be ok, if a bit dirty, without the harvested water.
Anyway, I like trying out new ideas so good luck with it.
:bathbaby::bathbaby::bathbaby::bathbaby: