NLS residue from Category D NLSs must be discharged to a reception facility or discharged to the sea using the following procedure:

1. (a) Before discharge begins, drain or flush the NLS residue in the tank's piping systems into the tank.
2. (b) After draining or flushing, discharge the NLS residue to the sea in accordance with § 153.1128 or transfer it to a slop tank and discharge in accordance with § 153.1126.