Or here is another idea that will not block the pump pressure.

Since it will always pump off the engine vibrations couldnt you just vent it back into the tank and let the oil loop over and over. Then to move the oil to muffler shut the valve to tank and open the one to the muffler. Maybe have both valves in line with one servo and use push pull to open one and close the other.

I never tried this just an idea but seems like it would work. Kind of made me want to try this out now since I just typed it..haha