My bilge pump hose runs up to the top of the transom Tutuapp 9Apps Showbox where I have a 90 degree barbed fitting that points over the top of the transom.
I usually wet a small towel/rag with the Lime Away and 192.168.100.1 192.168.1.1 just wipe down the stained areas and wait an hour or 2 to see if tough areas need another wipe down.