disassembly

Hi, I'm making a greenhouse frame with 3/4" Sch 40 PVC pipe, and I cannot figure out how to dry-fit these pipes into the fittings so that they are secure, but can easily be disassembled. I don't have any high-tech devices or power tools, so I'm really looking for a simple, low-tech way to solve...

I want to replace the sand and carbon media in the tank and reseal this older unit for my Dad. I've read all the threads here on this model and watched all the YouTube videos I could find, and have downloaded the Super S installation/operators manual from several sources... But none of them...