Love my little 3 gallon, been doing lots of small water changes instead of one big one (like a big gulp cup a day on workdays).
Keep nice well water from home in a couple of gallon jugs under my desk, when pouring the water into the tank I was really disturbing the substrate and plants (and probably freaking out the residents too!)
The tank is half under a shelf, so I can't top off into the HOB, and putting a cup in the tank (to pour into) isn't possible with how dense it is planted.
One cheap plastic serving
size spoon and a few minutes with a lighter gave me this, the filling spoon!
Just pour into the bowl of the spoon and it fans out and doesn't disturb anything.
Formed the tank hanger part around a chopstick. If you try this yourself be sure to get the plastic hot enough to bend under it's own weight almost or it will just break. Blow on it for a while or dip in water to set (no, I didn't dip it in the tank - a cup of unrelated cold water