Place bucket on counter. Find the biggest measuring cup or tumbler you have. Fill cup or tumbler and dump into bucket until you reach the desired amount. Or go fill from the shower or bathtub or even the garden hose.
You can use this trick I found on YouTube. Skip to the 1 minute 20 second mark https://youtu.be/5n3QhrO-AUk
Cut the side off of a gallon milk bottle so that the water can flow in at the bottom, then out the top opening. Put the bucket under the top opening and that's it. :) As long as it fits from the faucet to the edge of the counter, it will work. Wishing you the best.
If you can still find one-they used to make a short rubber hose that attached to a sink or bathtub faucet. It just pushed on and had a rubber end that fit various sizes of faucets. I guess you could consider it as an earlier version of a magnetic detachable shower head! You might find one in the bath section of a large home improvement store. I don't even know if they make these anymore!
Try using an inexpensive pool noodle to run water from faucet into bucket.