Ok. I have tanks on the main floor of the house, the basement, and in the garage.
I used to siphon them all into buckets and dump in the toilet. Refill bucket in tub and carry to the tank. When I got my 300 that got old....
I then invested in entire rolls of 1/2 inch hose from Lowe's to reach all the way outside or to the basement sump for those tanks down there. Still filling via buckets. That got old...
I ended up with a spare utility pump and started using it along with my hoses to pump water in/out of the tanks. Having to unplug the pump, wait to drip dry the wet end and switch the pump from tank to sink, sink to tank, and don't forget the hose! That got old!...
What I am currently doing is a pump in the tank with hose to the sink, and a pump in 5 gal bucket in sink with hose out to the tank. (I'm on a well and don't require water treatment!) It's pretty simple. Set up hoses and pumps, pump out tank, turn off that pump, go turn on sink side pump, wait 15-20 to fill, move pump and fill hose to next tank, repeat. It's still not the best setup in the world.
Moving to a new house soon with LARGE basement!!!! Plan to build dedicated water treatment station in one corner with one LARGE pump. I'm going to run PVC to all tanks with ball valve located at each tank. Each tank will have a siphon set up on it to drain off waste water. All I will have to is spin ball valve when ready to refill the tank!