Even better because we more likely have this in our house: Dawn dish soap.Just remember, roundup will kill everything.
As suggested 2-4d will just kill broadleaves but I don’t know what the consumer grade product is called. 2-4d will be listed as an ingredient. It will kill flowers, tomatoes, etc.
If you’re exposed to the oil, Technu soap is great. The sooner the better. And use cool water, hot water can spread it worse.
The worst case of poison ivy I ever got was in February. Installing a drainage outlet pipe in a ditch, apparently a root rubbed my arm and those oils are strong!
As soon as you know you have been exposed smear full strength Dawn on the area like a lotion. Let it sit for several minutes then rinse it off with cool water. Since it’s an oil, Dawn cleans it off incredibly well.
I did this when my young son went for a walk through grandmas infestation in shorts. Only the slightest reaction. And I think I missed that spot.