This can be washed as needed but take care to dry the area around the contacts (if fitted) on the back of the tray, particularly after de-scaling otherwise the machine will repeatedly tell you to empty the tray.
In fact it is better to remove the cup grille and empty the tray over the front and not over the contacts.
The used coffee bin sits on the Drip tray, There is no sensor that tells the machine when the bin is full - it simply counts how many drinks youve made and then requests that the bin is emptied. Each time the tray is pulled out (when the machine is on) even if you only have a quick look in it assumes youve emptied the bin and resets the counter.