so, i have a 6000l cylindrical tank that i am setting up as my pond and i have a question around the pressure in the pipes..

its an old water reservoir that i cut in half and the bottom of the wall has a 50mm reinforced threaded tank adapter. so i already have the setup and routing to the bio filter planned. basically the filter will be set higher then the wall of the pond and the water will flow back with the natural pressure.
now i have 2 questions.
1. what will the effect be if i reduce the 50mm to 40mm about half a meter above the bottom outlet?
2. will the pressure be able to push the water through the pipes up about 1.7m to get to the bio filter, or should i fit the submersible pump to the bottom outlet and push the water through?

hopefully somebody is watching this forum still that can help.