for fills use the paint bucket tool, not the ink bottle tool. (use a mouse hover to see the tool names.)
When you draw with the brush tool you can select an Object Mode, where each line is a separate object. You do that by clicking on a circle icon in the tool palette. If you draw that way the paint bucket won't be able to fill the area. You can solve that by selecting all of the lines that you want to fill, and do a Modify/Break Apart. Then it should fill ok.