Use the inpaint feature from the ControlNet extension, not from the img2img tab, it will completely replace the marked area and not get influence by what is already there. It's much easier to work with and basically works out of the box without any fiddling. If you want to preserve the pose of overpainted areas, ControlNet's OpenPose/Depth/SoftEdge/Canny can help.
is where all the models are, you have to make a login and enable "Mature Content" in the Account Settings if you want to see the porn models. Though even without that you can generate nudes, as many of the normal models will do nudes too, e.g.: