Just a thought... Iif you are markng an obstruction, write that on the bleach bottle as large as you can.
eg: ROCKS, SHALLOW, LEDGE, WATER-INLET, PILE, MOORING, EX-WIFE.
I believe you are also supposed to put your name and address on any bouy you install and they are supposed to be consisently shaped with the official bouy system (Back-top/Red-top, channel markers, hazard). I doubt you will get hassled over a bleach bottle though. Since private markers seldom make it onto a chart the bottles are a lot safer to hit than a spar or can.
Putting a little sand in the bottle will help it float upright and be a little more visible.