In article ,
Jeepers wrote:
water. So I lose the argument. HOWEVER... I also want to leave the hose
attached to the top fill bung so I don't have to re-attach a water
filled, running, hose back to the cabin.

And you have thus found the difference between engineering and physics.
Physics correctly states that it's less effort/energy to fill the tankt
throught the bottom hole. Engineering notes that it's not that much more
energy/effrot, and that there are other considerations in the practial
implementation in favor of the upper hole.

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