You can completely fill the generator with electrolyte if you want. Just understand, that you will loose a bit of electrolyte out the gas port once you fire it up. I have seen several folks who use their bubbler as a fill device/bubbler mounted above the generator. This allows for your generator to always be full. Word of caution if you do this though; make sure all your terminals exposed to the electrolyte are sealed. You can use heat shrink tubing or marine goop, but anything exposed will allow for stray current and a whole lot of heat.
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Some days I get the sinking feeling that Orwell was an optimist!