Okay.. Emptying the gmail trash from your android is not as cumbersome as it seems. For starters, it seems like a perennial conundrum, but It's actually quite easy. Let's make one thing clear: the trash folder CAN NOT be emptied from the gmail app!
Here are the steps:
*From your phone, using your WEB BROWSER (not the gmail app), log in to your gmail. Once logged in, you will notice that the layout from the browser is disparate from the layout on the gmail app.
*scroll to the very bottom of the page and select "desktop version"
* once selected, scroll back the top and hit the "empty trash" button. And there you go.
BTW, you do NOT need a laptop or desktop to perform this action. I have done my preliminary due diligence, and trust me, it works!
Hope this helps!