The white fitting is a broken off
spin welded fitting fitting for what is probably a polyethylene tank. It is either a 3/8 NPT thread or a 1/2 NPT thread.
The fittings have a flange and are attached to the tanks by boring the appropriate sized hole into the tank. The fitting is then placed in a
driver that is attached to a router. The flange of the fitting is placed against the hole of the tank and the router spins it at over 20,000 RPMS to melt it to the side of the tank permanently bonding it to the tank. You only squeeze the trigger on the router for a couple seconds or so and then let it stop spinning.
In order to do the repair you would probably have to scrape off the existing fitting material from the side of the tank until it's flat, then spin weld a new fitting into its place. If that doesn't work you will have to repair the hole in the tank then move over to a new spot, drill a hole and spin weld a fitting in the new hole. Another option would be to install a larger fitting in the same spot.
A new spin weld fitting is under $10. But there are 2 problems in installing the fittings. The 1st one is the driver that inserts into the router that holds the spin weld fitting costs from $75 to over $100 dollars and there is a different one for each size fitting. The other problem is holding the fitting with the proper amount of force against the tank and long enough for it to bond properly on the first try. So it might take some practice.
I wanted to add a larger fitting on my fresh water tank for a larger drain, but couldn't find anyone that could do it for me.
Video on spin welding tank fittings.
