I've always used the bleach in the water hose as suggested. But first I put bleach in the hose making sure that the bleach permeates the entire length of the hose. Then I flush the hose under as much pressure as I can get from the tap. If your hose has been in use for some time you might be surprised how much algae can accumulate and adhere to the inner lining of the 'sanitary' hose. I would repeat till the water at least appears to be clear. Best to blow that bleach loosened algae out onto the ground rather than into your tank.