Are you looking at the purple tub?
I got that 20 years ago at Revy. I think rubber maid makes one that is big enough to hold the 3cu ft promix bag.
It's a 1 time use.
I used to chuck all the used mix into my compost bins. But from now on I will toss it all into a 55 gal blue drum and let it bake in the sun till the roots are all broken down. https://youtu.be/SGhbMxtKtnY