RoundUp is the only safe way to get rid of it without touching it. But... it takes a LOT of RoundUp and is not cheap. Plus you will have to do it several times to completely eradicate it. PI has a very extensive root system that travels underground over large areas.
Dawn is good, but it's not so much what kind of soap you use to wash, as it's the scrubbing action to get the oils off your skin. You have to use a wash cloth or scrubbie of some sort to wash with, to rub the skin. Soap alone won't get the oils off.