I have 5 Rubbermaid tanks as part of my set up. Water trickles into the top
of each one and leaves through the drain. Muck would build up on the
bottoms and plug the drains so I added a elbow and 8 inches of pipe to the
inside of the drains. That way the water that leaves comes from the center
of the tank height rather than the bottom. I don't use a pump. My tanks
are stair stepped down a hillside. The water that comes from the bottom of
one tank trickles into the top of the next. I poured thin concrete slabs
for each tank to sit on. I found that the tanks would crack sitting on
dirt. Part of the tank would settle unevenly and a crack would form near
the top. Concrete slabs fixed the problems. My tanks are my filters
however they function as ponds too.