About the same...
When the discharge fitting is on the side or end of a tank, waste will remain in the tank to the level of the bottom of the discharge fitting or the end of the pipe, which about an inch. A p-trap won't change that because the waste can't climb over the "sill" into it. A pick-up tube can reduce the level to about 1/2", but still has to leave that much because the end of the tube has to be cut at an angle. However, even if there's NO difference, I'd go with all the fittings on the top of the tank, with a pickup tube on the discharge any time there's enough clearance above the tank to do it (at least 5"), because that eliminates any standing waste in a hose to permeate it. It also prevents spills if a fitting should fail, and makes re-hosing a LOT easier. A discharge ON the bottom of a tank results in a hose that's always completely full of waste...a p-trap is always full of waste...even a hose that's on the side or end and goes straight up to the deck fitting will stay full of waste to the level in the tank.
