pig launchers
Confined spaces may include but are not limited to tanks,vessels and pig launchers.
6 Answers
In Argentina we use the English word "pig" also, but I think you can say "receptor/lanzador de rascadores / raspatubos". In some countries are also named as "chanchos" or "marranos", but I guess that's local. The way I'm first suggesting should be neutral and easy to understand.
There are "smart" pigs and "dumb" pigs.
This one is definitely a dumb pig. 
You can see pig launchers and how they work in Alaska on the Alaska pipeline. I took the tour. It's really quite interesting. There are "smart" pigs and "dumb" pigs. Dumb pigs basically just rout out the system. Smart pigs cam detect pipe thickness and the amount of corrosion in the pipe, stuff like that. But in the demonstration in Alaska they show you how the system works and they have actualy examples of the different types of pigs.
Here is a dumb pig:
Here is a smart pig:
What it looks like:
What is a Pig Launcher/Receiver?
Pigging in the maintenance of pipelines refers to the practice of using pipeline inspection gauges or 'pigs' to perform various operations on a pipeline without stopping the flow of the product in the pipeline. Pigs get their name from the squealing sound they make while traveling through a pipeline. These operations include but are not limited to cleaning and inspection of the pipeline. This is accomplished by inserting the pig into a Pig Launcher - a funnel shaped Y section in the pipeline. The launcher is then closed and the pressure of the product in the pipeline is used to push it along down the pipe until it reaches the receiving trap - the 'pig catcher'.
If the pipeline contains butterfly valves, the pipeline cannot be pigged. Ball valves cause no problems because the inside diameter of the ball can be specified to the same as that of the pipe.
Pigging has been used for many years to clean larger diameter pipelines in the oil industry. Today, however, the use of smaller diameter pigging systems is now increasing in many continuous and batch process plants as plant operators search for increased efficiencies.
Pigging can be used for almost any section of the transfer process between, for example, blending, storage or filling systems. Pigging systems are already installed in industries handling products as diverse as lubricating oils, paints, chemicals, toiletries, and foodstuffs.
Pigs are used in lube oil or painting blending: they are used to clean the pipes to avoid cross-contamination, and to empty the pipes into the product tanks (or sometimes to send a component back to its tank). Usually pigging is done at the beginning and at the end of each batch, but sometimes it is done in the midst of a batch, e.g. when producing a premix that will be used as an intermediate component.
Pigs are also used in oil and gas pipelines: they are used to clean the pipes but also there are "smart pigs" used to measure things like pipe thickness along the pipeline. They usually do not interrupt production, though some product can be lost when the pig is extracted. They can also be used to separate different products in a multi-product pipeline.
Pigging in the maintenance of pipelines refers to the practice of using pipeline inspection gauges or 'pigs' to perform various operations on a pipeline without stopping the flow of the product in the pipeline.
Oh.... Good, to the point, nicely technical reply. Still, nowhere near as fun as what this kid here is doing for Scout points! 
Interesting word, I thought people were literally launching pigs, never heard this before
pig launchers: un émbolo tipo bala (“poly pig”)
