I sanitize the hydrometer & tube before taking the test sample. The OG one goes back in,since it's sanitized & ok every time I've done it. FG sample gets smelled & drank to see how things are coming along. As long as everyhing used for the sample is sanitized,dumping it back in (OG one anyway) is fine.
Everything works if ya let it-Roady(meatloaf)