Just curious... If you don't use your old water at all won' you create a cycle that will kill your tank?
I have moved/upgraded/combined my tank about 10 times. NEVER lost a fish. I always used 50% of the old water but tried to transport all the old water just in case.
Use trash cans and fill them 1/3 full. Flexible Rubbermaid or brute.
Water is just water. You can do daily 100% waterchanges if you want and will never have a cycle.