A distinction needs to be made between soap and detergent. Soap will not remove oils, you need a detergent for that. So washing clothes in a washing machine will work, it uses a detergent. But washing with soap and water will not work.
For washing after handling PI, I found 2 things that work well. Fels Naptha bar detergent can be found in the laundry section of hardware or grocery stores. I guess it used to contain napthalene, which will dissolve oils well. Now it doesn't so it's safe for household use. The fact that it says it's used to pre-treat clothes, and that it has surfactants in it highly suggest that it would be a detergent. The other solution I have had success with is Tec-Nu. It's a thick liquid that I rub on my arms and legs after handling PI, then wash off in the shower. Tec-Nu is expensive, $12 for a bottle but it will last for many applications and works well.