Traffic is an amazing thing here in Dar es Salaam. There is no way you can predict how long it will take you to get from one place to another. Because the traffic is always unpredictable. If you are stopped at an intersection people will walk between cars to try to sell you things. Pikipiki drivers drive between rows of cars to get ahead of everyone. Vehicles will go off the road to get around any number of cars and then cut in, in front of someone who has been waiting even longer. It is amazing what you might see when sitting in these long lines waiting for an opportunity to move.
We watched this guy for quite a while. He had plastic bags he was hanging on the side of the truck from the valves that release the gas. He would than empty it into a large water container. If the truck would move he would jump on the back of the truck and ride until it stopped again. We found out when we mentioned this to a friend, that it was okay. The trucks are coming back from "up country" where they empty their load. While heading back to reload these guys just empty out the tank the rest of the way before the truck can refill.