Please do the same for the turtle tank-filter through the bottom. Where is the water pump, inside or outside the water tank? The pumped water is directly put back into the water tank?

The pump can be placed anywhere, but it is usually placed on the cylinder wall. When the water is pumped out, it will pass through the filter barrel and then return to the tank to filter the biochemical cotton and filter cotton of the ceramic ring of the barrel, but generally only the filter cotton is needed, and the ceramic ring is placed in the tank (as shown in the figure).