This is one I made for a 10 gallon. It won't work for 1 gallon a day but I thought it might give you some ideas.
components:
1/4" vinyl tubing
Black reservoir container
Glass bottle (happens to be a Crown Royal Reserve bottle)
The tubing goes from the reservoir to the little internal sump I made for the nano.
The reservoir container is situated so the top of it is at the same level as the display tank. This is important to avoid overflows.
The glass bottle is hung upside down at a level so that the opening is at the same level as where you want the waterlevel to be.
How it works;
As the water in the tank evaporates, the water level in the little sump lowers. This causes water to siphon from the reservoir to the little sump. When the water level in the reservoir drops below the opening of the bottle water will gurgle out of the bottle and into the reservoir.
I filled the bottle and reservoir with limewater but your regular topoff water will work just fine.
