Please help - Black water holding tank damaged

You have to use abs to repair it. Youtube has videos of people making mixtures of abs shavings and glue to make a paste. I bought a kit on line which came with some cloth and the proper mixture of abs paste. The tank I repaired was only cracked around the fitting but it worked well.

It's called Plasti Mend and the web site explains it. I just posted one example of the different size kits. Getting everything very clean and not having water weeping into the repair area is important.