The air pressure method with a tire pump works pretty good. But you could use the one way valve squeeze bulb they use with small outboard boat motors too. You squeeze the bulb and it pumps fuel one way. Reverse it to defuel the tank. I remember years ago that most everyone was using the boat squeeze pumps with their airplanes. I still have a couple of them myself too.

But I prefer the hand crank pumps nowadays. I like to use Dave Brown's Six Shooter manual pump. For gasoline it is a bit more stiff than the glow engine version, but it works well. Albeit on a cold winter day it can be too stiff and not work as well. But the Dave Brown Six shooters tend to be ultra reliable and keep on working when others break..

I am also using a couple of hand crank gear pumps now too. They work pretty good too. Years ago they were prone to start leaking after a while, But the current ones do not seem to have that problem anymore.

I have used electric pumps off and on, but they have the disadvantage of needing a battery to run them with. You have a problem if the battery isn't working.

I liked the big syringes we used for fueling with, but the ones they sell do not do well with gasoline though as the rubber plunger deteriorates in them.
I would like to see a long tube device, like a long syringe plunger with graduated markings on the side. You draw the fuel into the tube pulling on the plunger up to the number of ounces or millileters you need. Then you connect it to the fuel tank and push the plunger down filling the fuel tank. I might think about it some more it might be a doable device for fueling and defueling a plane with. I could use a length of tubing, machine a plunger with some o-rings on it and thread a rod for it and put on a handle for it. Mark on the rod some fuel tank fill markings. Then fit the other end with a fuel fitting of some type for the fuel tubing.

The RC car people were about the only ones using a larger fuel cap on the fuel tanks. But for RC planes it didn't happen as usually people wanted a small easy to hide fuel fill/unfill method.