Hey guys.
I used the wrong term, actually where Milou sleeps is a house with a removable roof (dimensions 26x12 cm), this must be small then. Milou is peeing where he sleeps. I'm going to get a bigger cardboard box and also this month I bought a sand bath to see if he's interested in peeing there. Hope it works so I don't need to mess around with his nest so much. I took Milou several times to remove some poop from his fur, I was worried if he sleeping with so much poop could harm his health.
I had a hamster that flings out his poop the door of the house, I think it very funny, hamsters are very interesting.
Thanks so much for helping