Just took possession of our "new" boat and it's obvious the PO (otherwise meticulous in his maintenance) used Wesson Oil to "lube" the Raritan PH II. I'm going to replace the cheap hoses, remove the pump-overboard connection, install a head kit, and [hopefully] flush out the holding tank to clean out the oil previously placed in it. Since oil does such a fine job of sticking around, what is the best way to remove it? Would a detergent work without creating a residual also? Thanks! Michael O'