I would think that there should be a thu hull, somewhere at the stern the leads to a seacock and then to the pump. If all you have are drains, then you have no way to draw water in and therefore no pump/washdown installed. On a previous boat, I cut in the thru hull and added a pump to a prewired pump situation. Perhaps that is your setup? BTW look underneath the boat if you have not, some thru hulls are installed there as well.