assuming you mean you cannot connect the hose for whatever reason.... but just buy a 12v or 110v water pump on Amazon. Setup as external pump, attach hoses to feed through normal fill, put other end if hose in external container filled with water.
Depending on size if your external container it might take quite a few trip to fill it then pump it into your internal tank.
Sounds like you want some other idea but i don't see a simplier solution. Gravity fill has drawbacks including the installation itself which i didn't find appealing.
i opted for a 12v pump gicen new battery capacity and solar power over a 110v pump though might be handy to have both.
There are even a couple ready to use external pump setups on Amazon. they run about $75-$100.
I actually wondered why gravity fill and such an external pump option isn't standard equipment anyway.
