I usually bring an empty Gatorade bottle with enough detergent for a few loads of wash. The size of the bottle depends on the length of the trip, but the cap screws on tight so I'm not afraid of it spilling. Just for added security I put the bottle in a zip top bag in my suitcase. Works well and even if there is a little left that I don't bring home I don't feel like I have wasted a late amount.