Yeah the 5L one is the one I use, it was about $25 on its own so the both together for $13 is a decent deal from Aldi.I am assuming it is the 5L one that you use? Do you leave the cleaning solution in the bottle permanently, and just add to it as required?
I usually just make some up each time, either some PBW or just Sodium Percarbonate for cleaning, I think they are only active for a certain amount of time anyway so don't bother keeping. Most of the time I only actually do a litre or 2 as well, you don't use much really, just fill the lines, run a bit through, leave sitting 15-30 mins (depends on how long since the last clean) and then run some fresh water through, about a schooners worth or so for each tap.
For sanitising it's more of less the same but I don't rinse. I use star san for sanitising. Usually only make up a litre or whatever I have in my spray bottle if its not too old and enough to cover the dip tube in the sprayer. Otherwise I just make up a new litre which is usually more than enough.