[Nige]

If we borrow from RA-4 chemicals (idea) to use Distilled water to mix and then fill up the empty portion of the bottle with Butane gas, will that help keeping the T-Max Developer longer ?

that may help but as mentioned above, don't dilute it until you want to use it and only dilute how much you want. Say your tank holds 500ml (I work in metric!) and the the dilution is 1+4, then pour 100ml of developer into mixing container and add 400ml of water (ideally tempered to suit temperture required). Use once and dispose of.