Michael, how are you going to do a Cetus Sieve on a gravity flow BD?
No very easy, only way to do one was what Bill said has been done by the EA team but you'll need to split the line from your bd into the Sieve & then using another pump to bring that water back into the Nexus. This will end up costing more to run it since you'll need a sieve & another external pump.
Bill, hope you don't mind me posting this pic: