Those that get away with doping are seemingly just as sophisticated as the testers. Take Lance Armstrong as an example:
From National Geographic online:
Athletes have, along the way, figured out how to beat tests. The most high-profile case may be that of Lance Armstrong, the seven-time winner of the Tour de France. Earlier this year he admitted that throughout much of his competitive career, he doped strategically to avoid testing positive for performance-enhancing drugs. Rather than inject EPO moments before a race--where he knew that testers would be waiting at the finish line--the cyclist scheduled doping during training rides and between races. Working with a group of physicians, some of whom may still face prosecution by federal investigators, Armstrong was also able to keep track of when certain substances would appear in his system and how quickly they would metabolize.
I walked away from the article thinking that those sophisticated to pass tests via timing, off-label, or non-existent usage of some forgotten steroid is mostly done by those that have the most money to gain.
Is swimming clean, NO WAY! But I will say that the majority of swimmers in the United States don' have the income or the infrastructure to finance a medical team of dirty doctors, dirty coaches, and "bag men" to pull it off. Must or all will get caught.