Normally I dislike the SSPX for their schismatic tendencies, but they have a few articles that are good that refute the lies and ignorance of Sedevacantists (who plagiarize each others lies). Here is one on the validity of the Ordination of bishops by Pope Paul VI. Note most sedevacantists never bother to actually read primary sources or look into an issue besides plaguarising people like the phony "Demon Bros." Here is the link showing the validity of the rite http://www.sspx.org/miscellaneous/sedevacantism/validity_of_episcopal_consecrations.pdf
It shows the rite of ordination of Paul VI is restoration of an older rite used in the early Church taken from the "Apostolic Traditions" by a Hippolytus. Some may argue that this document contains a rite never actually used, whether that is true or not, it is true that the Copts and Maronites has historically used an almost identical rite of Ordination--and their bishops validity was NEVER questioned.