There was once a time when the UAT didn't even exist (It's true, it's true).

I flew my first two turbine powered models with three 40oz tanks in series (one was an operational drop tank) with no special air trap of any kind. Worked great, I put several hundred flights on each one of those airplanes without any problems.

I do have UAT's installed in two of my models today simply because it is cheap insurance (and they are BVM airplanes so they came with the kits). In my little PMP Gripen there was not room for a UAT, so I installed a Sullivan 3oz round tank with a pleated paper clunk. It cost a fraction of what a UAT does and works just as well.