With algae scrubbers, the key is flow and lighting

For a 150 gallon tank, a algae scrubber would need to be about 12 inches by 12 inches assuming it is lit from both sides with the correct amount of lighting. That would be 144 square inches of screen which would need about 500 gph of pressurized flow to force it through the tiny slit the screen also fits into. You will not get that from a drainage line unless you are putting around 1600 gph through your tank which is far to much for a fresh water set-up. You have to keep in mind, a scrubber will add at least some pressure to the line that supplys it.

If you read through the last link I posted it should a little more clear to you than how I must be explaining it in this thread