Yeah that is definately Sue T - She's a veteran and she's had to do it a couple of times, making it a bit more "common" for her. This is especially common to do when you're dealing with pinched mantle (a very serious disease). If you had to dip at all I would do a saltwater/iodine dip.
Its difficult to dip a clam for a number of reasons. Hitchhikers can sometimes be protected by the clam during the dip, when the clam closes up, or by the hitchhiker being wedged in the byssal opening.