The UAT is there to make sure that you don't end up with air bubbles in your
fuel supply to the pump & engine. Too many bubbles & it's dead stick time.
There are alternatives like a simple header tank which does the same job.
Or, you can use a felt or pleated paper clunk which hold a little fuel if the clunk
should lift out of the fuel.
If it was me, & you have room, fit one.
In theory the UAT should remain full of fuel while the model is flying.
If you do fit one remember to fill it with fuel before you check the
model's CG. You can use them for ballast to adjust the CG. - John.