>sataa kuin Esterin perseestä
"It rains as if from Esteri's asshole"
It rains very heavily. Esteri is a woman's name and probably implies and older woman, but it's hard to say with such an old idiom.
I think Finnish has a lot of these pretty weak idioms where you just add dirty ideas to everyday occurrences, instead of saying something clever or timely. I'm pretty bored with them so I haven't developed a good memory for such things.

But then we also have words like "a reindeer's pissening" which is just the measure of land for how far reindeer will walk between two piss-breaks.