Husband and I had to completely re-do our gray system, plus our vent. I published a multi-post set of instructions
here.
Your Class B model is different, but the principles are all the same, and you will be able to use comparable parts.
It's an important job to DIY. Repairs similar to the ones I describe in those posts are generally north of two thousand bucks assuming you can find a repair shop to do them. It's unnecessary to pay prices like that. This kind of plumbing is a pain in the butt and time-consuming, but very do-able with instructions, when you don't have to re-invent the wheel.