get a totally sealed container, and have the pipe or hose set about half an inch or a quarter inch under water, then evap and gravity will do the rest.
This is a great thread because this is something I need too. I want it for an ATO system so that my skimmer works at its prime. I've been losing 1-3 gallons a day. I don't know why the fluxuation. My question:
Would a 5 gallon dosing container work if you didn't unscrew the back
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that lets the air in ? Then all you do is make sure the line is at the point in your sump that you want the water level ? Do auto top off pumps syphon water in if the power goes out ? Whats better ?
Here is my really cheap bucket. It is a little ugly sitting next to your tank but if your leaving for a week nobody will see it and then you can just put it all away until needed again