What step did SFC Green forget while preparing the latrine for a urinalysis test?

The correct step SFC Green forgot while preparing the latrine for a urinalysis test is posting a sign. Posting a sign is crucial as it informs the soldiers that the location is designated for urinalysis collection, establishing the importance of maintaining the area for the testing process. The sign serves to ensure that all individuals are aware that urinalysis is being conducted, thereby promoting a respectful and orderly environment during the testing. This action helps to prevent any confusion or unauthorized access, which is vital for the integrity of the testing process.