They did two tests on the "sucked down with a sinking ship", one small scale tank test and one real life with a 30ish feet steel boat.

The tank test was a lot of fun. Adam sat on top of a small weighted container, and followed the container to the bottom when they released it. Seemed to reinforce the myth..

Then they bought the "Mythanic", sat Adam on top of it and opened the bottom valves. Adam got scared in their first attempt, and jumped off to early, but could not feel any pull from the boat when i sank.
They raised the boat with a large harbour crane, and sat Adam on top of it again with open bottom valves. This time Adam sat on it until it sank, but he could still not feel any suction or pull as the boat sank under him.

Their conclusion was that the myth was busted. They explained the tank test with using wrong scales on the surface area and weight of the container Adam sat on.

I think they would have gotten a different result if "Mythanic" sank faster instead of the slow pace they could manage. I still think it's a good idea to get away from a large ship sinking.

Adam and Jamie are the hosts of the show, both special effects guys. Mythbusters is a great show in my opinion.