Use a garden hose to siphon, put a piece of sponge on the end in the tank, run it downstairs & siphon the water out. Get an adapter for the sink if needed, use the same hose to fill.
I have over 30 tanks & 1,000 gallons in my setup, it's oriented mainly towards breeding angels. I do 50% weekly on the bigger tanks, larger water changes more often on the smaller tanks. I gave up buckets long ago, I use two hoses in the fishroom, one to drain, one to fill, both running at the same time.