When my son and I were pushing the Avalair back in the shop the other day, we hooked the gray water drain on my rototiller. Basically, exploded the down spout.
I had to make an access hole. This is not the finished product. I'll square it all up and finish it out, then make a cover for it all.
I decided to standardize the outlet to accept the regular sewer hose, due to the fact that most campgrounds require a donut on the hose going into the ground.
I bought the fitting from Camping World. I carried it into the local hardware store. I found a rubber bung that is stepped and tapered. It is mainly used in non-pressure situations for drains etc. It fits pretty tight. I forced it in and then cut the end off to allow enough clearance for a close out cap. Then I painted the pipe with plastic paint, hoping that it may not be super noticeable.