Black tank outlet repair

That is NOT ABS. Also no RV uses 4 inch pipe. 3 inch pipe is the largest size. There should have been a hose clamp that held the previous fitting. Get this fitting It has the O ring to slip inside your tank exit fitting. Then use the Sikaflex around the seal and then use 2 Hose clamps and let dry for 24 hours. Doug

https://www.icondirect.com/holding-tank-fitting-3-hub-fitting/

https://www.homedepot.com/p/Sikaflex-29-oz-Self-Leveling-Sealant-Gray-7116080/300934522

That tank doesn't look like ABS. Maybe try shaving a few slivers off it and see if they dissolve in acetone. If they dissolve they are most likely ABS.

If ABS then yes use black ABS glue available at any home improvement center. put glue on both the pipe and the tank and slide the two together with a slight twisting motion. Then let is sit 24 hours before messing with it.

So, it looks like a pre-formed outlet that the black drain pipe attaches to, and I'm assuming 4" pipe. However, I can't tell if the 4" is the outside or inside diameter. Either way, black ABS glue should go on the inside or outside of the outlet and the drain pipe attached. If it broke off because of stress at the joint, I would add three stainless screws around the outlet/pipe, but shorten them lest they provide a catch point inside that will catch TP.