There was some discussion of these devices on a previous thread, "Public toilets" I have bought (but not yet used ) a pack of 3 "Travel-John" These have a top like a shewee, but attached is a bag containing very absorbent crystals, so it does not need an outlet - you can use it in the privacy of your own tent, car or broom-cupboard, and throw it away later. It is said to hold 800 mils, so as it stays dry inside as well as out and cannot leak (they say!) you can reuse it if necessary. It has a kind of zip at the top of the bag. I bought mine on Amazon but they are on sale in various places on the net. The reviews by ordinary users were highly complimentary.