Has anybody used or heard of baking soda being periodically run thru the heads and lines to help keep the system fresh?
Vinegar. But let it sit in the lines as long as possible. Otherwise diluted muratic acid if the hoses are filled up with mineral deposits. Does your head/s use salt water to flush? If so, and if there is no strainer on the incoming flush water line, organic matter can build up in the bowl rim and rot causing the head to stink. In that case, you need to take the bowl off and flush the rim out real well and then install an inline strainer on the in coming flush water line so it would happen again.