I googled "Saastainen Kaste", and it seems to be a song of a Black Metal band named Horna, and from the lyrics:

...saastalla ja halun kasteella...

...with filth and dew of desire...

... I conclude that "Saastainen Kaste" means "filthy dew", but not the normal dew that is on the grass, but sexual "dew". I cannot really translate anymore of the lyrics, as it would be against the AW Code of Conduct. I don't know anything about the band, as I've been living in the US since -98, and I don't much listen to or care about Heavy/Black Metal anyway.