PVC Pipe into Hub is sealed with oakum. I use to have Hercules Plastic Seal around that, but i have changed some things and have not got any more yet. The pipe you seein the picture is the main stack on the left, and the pipe with the drop is for the washer only, it rises up out of the picture where the washer hose hooks in. All of this is in the basement, the picture and the washing machine, so it's all below the toilet b/c thats on the first floor, draining into the main stack above what you see. Does this mean that the drain in my picture needs to vent up and into the main stack above where the toilet drain enters the stack? What about an Air Admittance Valve for the washer drain, just after the trap before it enters the stack? or is that completely wrong?