When I've been playing in the poison ivy, I come inside by way of the laundry room, put everything I'm wearing (including my hat) in the washer and then run for the shower. I bought jewel-weed soap at a local outdoor store (soap was made in NC or TN, I think), and I scrub all over with it. My sunglasses come into the shower with me and get cleaned, too.
I still remember a bad case of PI I had in 1982, and am paranoid of ever getting it that bad again.
My brother swears by Tech-Nu, but to be really effective, you have to put it on FIRST, so it forms a barrier between your skin and the PI oil. I'm way too spontaneous for that.