Professional rainwater harvesting assumes that you need about 30 watering cans of ten litres each in three weeks. A rain barrel capacity of 300 litres is therefore sufficient.
In addition, this calculation must take into account the size of your garden, the weather conditions and the amount of water required by your plants. If you have the privilege of a very large garden, I recommend a larger rain barrel.

This varies from manufacturer to manufacturer. You should inform yourself in detail about the frost protection of the rain barrel before buying.
Generally, it depends on the area you live in. If you live in places where a lot of frost is to be expected, you should empty your barrel. Otherwise, the rainwater can remain in the rain barrel throughout the winter.
However, it is important that you do not fill the rain barrel to the top, as the ice can expand and cause damage.

You have two options to choose from. On the one hand, there is the inexpensive option, whereby you simply take a piece of hose, cut it to size and suck in the water from one barrel. As soon as the water runs out of the hose you put it into the second barrel. The water level will adjust automatically. If you want to connect more than two barrels, you will of course need several pieces of hose.
On the other hand, you can fall back on the professional version. There are special rain barrel connectors for this, which you can get in any DIY store, garden centre or at Preis.de.

After mosquito larvae have hatched, they sit on the water surface for some time. However, they need the right surface tension for this and you can destroy this to get rid of the insects.
For example, vegetable oil or washing-up liquid is suitable for this. Simply add a few drops to the water-filled rain barrel and the mosquito larvae will die.
You also have the option of buying special preparations to combat mosquito larvae.

A rain barrel pump is specially designed for use in the rain barrel and has several advantages. It has a pressure of over one bar, so that the transport of water through a long hose is no problem. In addition, it has a riser pipe that delivers water directly to the top and a shut-off valve that makes it convenient to stop the flow of water.
However, if you need even more power and have adequate storage facilities when not in use, I recommend a garden pump or a domestic water pump. You will also need to provide a place for these pumps that is protected from the wind and weather. In addition, the high effort of commissioning is to be considered with these pumps.

Small cracks can be repaired with a special glue. In case of a bigger damage I recommend you to buy a new barrel. The effort and the costs for material are about the same.

You can put a plastic rain barrel in the bulky waste or take it directly to the landfill.
If it is made of metal, you have to dispose of it via scrap metal or scrap metal. Here, too, you have the option of taking it directly to the landfill. Under no circumstances should the metal rain barrel be disposed of in the household waste. This can sometimes lead to the waste disposal company refusing to collect all the waste.