What other sensory experiences are on offer in the nursery that might provoke this child’s curiosity? If he is sensory seeking and has a higher threshold for what will meet his sensory needs than the other children in the nursery then the ‘usual’ sensory experiences such as sand and water play might not be quite enough to meet his need. I had a situation recently where a child was chewing a lot of the toys in a nursery to the extent where they were regularly being broken. When I looked around the nursery it was beautifully resourced but there was nothing that quite hit the mark for him and so chewing on toys was the only thing available to him to meet those sensory needs. The nursery then invested in a few sensory toys and set up a sensory area and he absolutely loves this. The chewing of toys has virtually stopped as he is now engrossed in exploring the textures, lights and sounds of the new toys. So I completely agree with the above strategy of valuing and investing in the emptying routines (in a way that is feasible for the setting) but I wonder whether he can be introduced to some other highly stimulating activities which will enable him to engage in a wider range of sensory seeking behaviours (some of which might be easier for the nursery to manage).
I think your point about looking to see if there are events or situations that trigger this will help staff to work out whether his actions are purely sensory seeking for pleasure or a coping mechanism to deal with stress. Depending on which it is, they can invest more time in either preventing the stress in the first place through changing the environment or providing more opportunities for similarly pleasurable activities (or both!).