The main idea is really about rolling around in dense populations of phages. They can be found in huge quantities in dirt and seawater. For seawater you're probably going to get mostly fish phages and the like but dirt from the ground are going to give close exposure to a very wide range of different phage types.

So it's not about getting dirty so much as going directly to where all the main phage action is. You're not typically going to get a lot of this if you're stuck indoors all day etc.