Hi, just want to add something, since pixiv is a japanese site you will have to censor the genitals, just like a hentai manga where you see black lines over their genitals. You can't post uncensored images, doing so will get your account banned, it is necessary to abide to japanese censoring rules when using the site. To be safe read their guidelines before posting if you're unsure.
My best bet on posting totally uncensored content would be twitter, just as long a you mark your media content as sensitive.