Encore,
Been there done that...
Go to the hardware store buy a tube of GOOP, and some 320 sandpaper. Clean around the fitting with isopropyl alcohol and a Q-tip, scuff up the plastic with a swatch of sandpaper, apply the Goop to the nipple, it will sag down onto the tank. Unbelievable pressure capacity and it will last for years. I don't ever remember ever having to replace a nipple meaning unscrew it from the tank. This is a good looking, and lasting repair. Give it 36-hours to cure to pure elastic.