We had water in the cutlery tray and Yann found that where the drain is for the sink, underneath there's a cylinder and the base unscrews. The washer in this seems to be the problem here. What do I google to find a replacement? i've got no idea what these things are called

https://www.jacksonsleisure.com/caravan-...ng-ac530-ac540/

thank you, John.

Remember there are 2 sizes, I thought ours had gone, so changed it and then found it was a pin hole in the sink itself??