Bathroom sink use

[ScottishHaggis85]

My housemate seems to be rinsing off their used dishes in the bathroom sink (1 bathroom shared use) Im finding crumbs & the odd tiny bit of food stuck to it. It’s pissing me off tbh.
What would you do?

I’d ask them why they were using the bathroom sink, and then ask them to please make sure the sink is clean afterwards if they do that.

Thanks it’s just
uneeded as it’s a small 2 bed house with the kitchen just downstairs and always an empty sink to use so not sure why