A stovetop percolator diagram. Basically just a kettle, with a pipe leading from the bottom to the top of the boiling chamber, attached to a filter basket where the coffee sits. Boiling water bubbles up through the tube, into the coffee, drops down through the filter basket back into the boiling water.
https://kolektiva.social/system/media_attachments/files/110/246/639/030/576/139/original/7f293217e835938e.jpg