i recently bought a new H20w tank and when hooked up it failed to fill with water. I removed the "tee" and inside the tank inlet elbow I saw a piece of black plastic protruding down into the elbow. Seems as if it shouldn't be there. Is it a deflector or as I suspect, something that doesn't belong?
Can we assume you are talking about a water heater? In the nipple on top of the water heater are plastic inserts called heat traps (google "heat trap nipple"). They act like check valves to keep from losing heat due to convection currents. If you pipe the water heater backwards they will prevent the tank from filling.
Coastal South Carolina
This is a water HOLDING/PRESSURE tank for a well-water system.
On looking more closely i see what appears to be a plug that MAY have been unintentionally left in the tank by the maker. It (the 'plug') has two 'prongs' which look like they need to be squeezed together and then the plug can be removed. I just wish to be sure before i go to yanking on something and causing damage .... Thanks, Joe