In a house in Denmark I needed to clean the water trap in a floor drain looking like the one in the photo. (For some weird reason, these kind of household tasks always end up on the male… But that is another discussion :).)
I wrongly made the assumption that I needed to unscrew the four screws. Bad decision! This made the upper and lower part of the water lock to separate and the lower part fell into to the waste water pipe. Fortunately there was a bend some 30 centimeters down so it stuck there and I only (!) hade to put my arm into the pipe, grab it and pull it out.
To get the water trap out was actually more simple than anticipated. This how it should have been done: just put your gloves on, stick two fingers in the big hole and a thumb at the edge and pull. When removed and safely away from the waste water pipe, the four screws can be unscrewed in order to separate the two parts of the water lock so it can be cleaned more easily.