While there are lots of high tech ways to do this, I find low/middle ground works better for me as there are fewer "oops" situations.
With water coming in from outside at temperatures that vary and not wanting to invest in temperature compensation valves, I went to a reserve water barrel. Around here 55 gallon plastic barrels sell for $15. I fill the barrel, let it set to come to room temp and then use a small pump to fill the various tanks. A remote switch on a tether makes the pump control simple and easy.
For draining with the drain already there, I would add a simple standpipe and do the syphon cleaning as normal except you don't have to haul buckets.