If you look on Amazon and look at the 70gal tanks they show a drain and plug. Maybe smaller models do not have them. I have a 300 gal and a 70 gal and both have the drain and plug.
Look into the Rubbermaid stock tanks. They come in different sizes and have a built in drain plug on the bottom side for easy draining. I have a 300 gal that I use to overwinter some koi and I have 100 gal that I made into a pond filter that I have been using for few years now and they work...