I believe it is ABS plastic. You could use ABS solvent/glue from the lumber yard/plumbing supply places. If you make some ABS shaving by cutting some ABS pipe, and mix it in a glass mason jar with the ABS glue, put on the lid and let it sit a few hours, it makes a really strong paste. Use a putty knife or paint mixing stick to spread it. You can use some screen material for reinforcement and create a really strong repair. I used this method to repair my front gray tank that had two cracks, and it worked amazing! Here is the video I started with:
https://youtu.be/N2rVLU3bDMY I did not drill holes like the video, I did two patch layers. The first about an inch or two wider than the cracks, the second layer an inch or two bigger than the first. Good luck.