Waste water outlets

We have just bought a secondhand caravan and are unsure of the water outlets. There are 3 the left one has flexable pipe the middle soliid pipe and the right one fle xible pipe.  Could someone please explain what these pipes are connected to in the caravan. We know that we connect a pipe to drain into waste hog but want to make sure we connect the right 2. Sorry ifthisseemsastupid question but we don't want to make a mistake and ruin the pitch. Thanks