For cleaning and maintaining the chain and the gear wheels you can use some lukewarm water and a brush. 

First remove the worst dirt with an old cloth. You can also get a special chain cleaning set.

It's important to grease the chain immediately after cleaning. For this, Roetz uses Cyclon Law Lube chain oil, which is suitable for wet weather conditions. Drip a little oil on the whole chain and let it move in for a few minutes. 

After that, take off the remaining oil with a cloth.