Black Water Tank removal

[snorzz]

I have a 2013 Salem Grande Villa 407REDS and I want to remove the toilet and black water tank and install a conventional house toilet. Unbolting the tank from the frame and unhooking the drain lines is straight forward but how do you remove the vent stack from the tank and the toilet floor flange. Are they threaded into a fitting on the tank or are they glued to the tank. The dealer that I purchased the unit from claims that they have not removed tanks and that they do not want to do the work or give me any advice. I have read on other forms that the tanks are supposed to be removable by code. I have not found any standard which specifically says how the vent and flange are connected. Any advice would be appreciated. Our unit does not move and a house toilet has worked very well for us on our previous unit so we would like to have one again.