Since day one, 3.5 years ago, we have followed the advice of our dealer at Ship and Sail in Kemah and flush with freshwater from our tanks. It has never been a problem since we always seem to have plenty of water. The dealer said the water in the marina is 'ALIVE' with stuff (critters) we don't want in the holding tank and would prevent salt buildup and stuff growing in the intake lines. Using city water, we don't have problem with that 'black stuff' that comes from the inlet line when you flush that I've noticed on other boats that flush with raw water. And just a month after getting the boat, I read your posts here on HOW about KO and have been using it ever since. We flush by putting water in the head sink and I installed a tee in the sink drain line and a tee in the head intake line and connected the tees with a valve and I leave the sea cocks closed. Works great. Question, HOW does the chlorine in the city water effect KO? Sometimes I get a rotten carrot odor so maybe the chlorine is killing the KO? BTW, on our Gulf crossing we used sea water. Thanks for all your help over the years.