I tested Diamine Imperial Purple in a reused Sailor cartridge before putting it in a demonstrator, and the result was a stained cartridge. I love the color, but I haven't had any luck getting it out of my cartridge with water, soap, a little bit of ammonia, and time.

I don't write much, so a pen could stay inked up for months on end.

Is there a way to get this color out of plastic? Is it safe to use in converters and demonstrators without staining them too?