You're probably right about the connecting of the two ponds with the preformed piece, but I need to be able to get the water from the upper pond to the lower pond. One of the ponds (the one that floated) has a U shape cut in one edge. So I need to make some kind of lip there to channel the water back into the lower pond. Also if I make an outside tote filter then the water leaves the lower pond via the hose enters the tote and then leaves the tote via a hose into the upper pond. Is that correct?