Where I put the liquid depends on where I am. If I’m out in the mountains, I pour it outside. If I’m in town, or somewhere with a bathroom available, I pour it into a toilet. Yeah, you’ll need some sort of container to collect the liquid; which one depends on taste. I keep four empty plastic peanut butter jars in a small rectangular plastic tub with lid. The tub fits into the step area of my van, so it won’t tip over while driving (or if I kicked it). The whole small tub fits into one of those reusable fabric grocery bags, making it easy to carry it into a store bathroom without looking too weird. The jars get cleaned daily of course.
BTW, the jar used while doing the other stuff should be a shorter one, so it doesn’t get in your way so much.