In my keggle, I cut a small hole in the bottom, inserted a long bolt, welded it to the keg. Then i put a hex coupling on top of that bolt in side the keg. I got a stainless steel colander, cut a hole in the top of it. Put the colander inside the keggle and on top of the hex coupling. Take a eye bolt with a wing nut attached to it, thread it through the colander and into the hex coupling. Then tighten down the wing nut. This secures the colander very tight to the bottom of the keg.
Also, the colander has a hole cut into the side so a dip tube can be placed inside of it.
Obviously the colander is a dome shaped, not your normal false bottom but it works great.