Rheem-Rudd water heater parts list 2009 shows a short heat trap tube that extends down into hot side on some electric water heater models.
Length is unknown. Purpose seems to be the heat trap washer.
It is called “hot outlet trap” and/or “hot outlet heat trap or Dip Cup insert” (Kit) item number SP20003
Rheem 2006 Parts list and 2010 Parts lists show same kit on some electric water heaters. Part number SP20003 or AP12992