Had a quick question about breeding, I have what I thought was Synodontis Petricola but were identified as Synodontis Lucipinnis thanks to the help in these forums

I have been reading up on how to get them to breed, and am a bit confused, what is the purpose of the black marbles at bottom of clear bowl with flowerpot over it?
In nature, where or how do these guys reproduce? Black marbles just seemed strange, the clear bowl is just for watching for the eggs right?
They need to be watched and once there are eggs pull the bowl and tumble till born right? Ok then, how in the wild do the eggs get tumbled?
Also what is it with flowerpots, just an easy hiding spot cheap that wont effect the water chemestry, I see many clay or terricotta pots used in many pics and tanks and always wondered why is there anything to the coloring or something too or just the hiding spot/privacy it gives?
Just seems like there could be a much cooler looking breeding cave made and never understood the black marble thing.
I have 3 (sex unknown) just hoping one is female of the 3, all are about 11-13 months old by best guestimate. I want to get more of these but they are a bit expensive and not so easy to come by.
Was planning on giving them a dedicted 20 gallon tank with 2 breeding "pot" design units, then have a 3rd here to swap out one or the other every so often to keep things clean and such.
Do you just peek in with a flashlight and look for tiny eggs at the bottom of the marbles?
Lastly diet wise, I read black worms were fed, if I do a dedicated tank for them here like I described, should I try black worms? I have these 3 in a regular cichlid tank currently and it seems like they eat and grow fine off the variety mix of foods I feed those fish...
Thanks for any help and or answers/suggestions, links to good pics and info more about breeding etc.
Bill
