A Scow is a robotic waste transport ship. You can use a scow to dispose of waste in a star. If a Scow is used in this manner it is reusable and will return to your planet after disposing of its load. Disposal of waste into a star can be automated by use of a Waste Chain which requires the Trade Ministry to set it up.
You don't have to do anything to fill the scow with waste. When you send it to a target, it automatically fills with waste. However, you can not send a scow unless it can be filled to capacity. Scows can now be sent only partialy full.
A Scow can also be used to throw waste at other people's planets. Scows were not originally designed as weapons of war, so they do not have a stealth attribute. Their combat levels are not very high therefore, they can easily be destroyed by defending ships. If the target empire is paying attention and are able to handle the waste, then you might be giving them free resources. However, if they are overwhelmed then you will pollute their planet and make their citizens unhappy.
There are now a number of different types of Scows and they require both a minimum level of a Shipyard and Waste Sequestration Well in order to be able to build them. Scows have also had the new Berth attribute applied to the newer versions of the scows.
The types are: