BrassCraft 18-in 3/4-in FIP Inlet x 3/4-in FIP Outlet Copper Water Heater Connector in the Appliance Supply Lines & Drain Hoses department at Lowes.com
Flex Connectors for Copper Piping from Unisource Manufacturing
Piping and plumbing fitting - Wikipedia
MECCANIXITY Tee Y Type Copper Fitting Welding Joint Split Union Intersection 16mm or 5/8 Inch ID for Water Pipe Plumbing, HVAC, Refrigeration System, Pack of 3 - Amazon.com