Not having access to the taps in the laundry room is a shame; that would have been the easy way.
When I used the under-counter added taps, I just attached the hose to the 2-in-1 mixer gizmo, put the other end of the hose (with a simple garden-variety shut-off nozzle on it) into the sink right there, ran the water into the sink while I adjusted the temperature to where I wanted it, turned off the nozzle, moved the end of the hose into the tank in question and opened the nozzle to fill the tank.
I also used that same hose to drain the tank; put a T-fitting right near the sink faucet, with a shut-off valve on each arm of the Tee. Run a short hose from the faucet to the Tee, run another hose from one side of the Tee to the tank and run a third hose from the other side of the Tee to a bathtub drain, toilet, out a window, etc. Shut the valve leading to the drain, and use the faucet to fill the hose to the tank. Then shut the valve leading to the tank, and fill up the other hose leading to the drain. Finally, open the valve to the tank, shut off the faucet and close the valve leading to it, and you now have a siphon running from the tank, through the Tee and out to the drain.
I used this type of set-up for years in one house, and the hardest part was coiling/uncoiling the hoses. The rest of the water change was just a matter of opening and closing the appropriate valves and faucets. It's even easier if your tanks are in the basement fish room, like mine now are...because I don't coil and uncoil the hoses at all, I just leave them set up and clipped to the tank stands and the walls behind. I have two small tanks, totalling maybe 40 gallons of water, upstairs in my house now...and they require more time and effort to do the water changes than the roughly 900+ gallons down in the basement.
I'm currently in the process of surreptitiously running hoses from those two tanks, through holes drilled in the floor in concealed corners, to join up with the basement system. If my wife ever finds out...my postings here may come to an abrupt end...
