Most of us have just done a fernco and pvc. The fancy ones have put an ebay or similar snorkel head on the top of the pvc. Not sure if anyone sells a specific kit for the P500 or the P520 at all.
If you are going to snorkel the unit, I suggest looking at some videos on all the things you might need to consider. Here is one to get you thinking about the process on a 500 which is very similar,