The norm here and it mainly applies to older vans but will apply to anyone, is that it is caught in a bucket and put in to the dump point if in a van park. Often in caravan parks ofter have a drain near each camp that you connect a waste pipe to the van and run to the waste point and it empties straight into the drain. On bush camping it is also polite to collect in bucket and take well away from other campers to dump. There are some parks and that will not allow you in unless you are collecting and taking all rubbish and that includes grey water.