Just another relatively plus point about winebags. You can practically empty them completely by keeping the tap open and carefully tipping the box. Being a Scotsman I regularly do this with wine and end up with maybe 10ccs left in the bag. The same applies to dev so really no waste at all. In fact if you run out and still haven't got the amount of dev you need and its time to re-fill then you'll have to take the bag out anyway and prise the tap off when you can then empty the bag before refilling by squeezing the reamains into the neck of the tap. I'd estimate that you might have to waste about 2ccs when you rinse out the old developer. You might even simply re-fill provided it's the same dev of course. 2ccs of old DDX in 1L of new isn't going to make one iota of difference to the potency of the new stuff when you add it to what you got ready for the developing tank from the "old" DDX.
Pity we don't have 5L winebags here as in OZ then 5L containers of fixer, print developer and 5L of powder ID11 could go straight in one box.
Time we got more serious about wine drinking is what I say.