Well letbs get into the chemistry of your marine head. Urine contains uric acid. This reacts with calcium and other metals in sea water to form insoluble calcium salts. This is a solid so it then precipitates out of the flush water. If you donbt flush enough (and none of us probably do) then the calcium salt sits in the hose and forms a coating on the hose. One easy solution is to use fresh water flushing toilets. This uses your precious fresh water but doesnbt form salts (no calcium) and as importantly doesnbt bring sea critters in who can die and stink. Flushing a cupful of vinegar once a week (I think that is what Peggie recommends) allows a weak acid solution to sit in the hoses. This acid reacts with the calcium salt and resolublizes it. Donbt pump any more water than is necessary to push the cupful of vinegar down. You want it to be as concentrated as possible in the hose. This weak acid can remove a very thin film of salt but if it has built up to any thickness then it is too late. What can you use instead of vinegar? Well Peggie probably would not agree to anything else as it may harm the head. If you are brave you can use maybe a 1/4 cupful of Rydlime, CLR or Lime Away, all of which are stronger acids. If you have a heavy layer of scale built up on your hoses the only solution is either to replace them or take them out and beat them and work them back and forth to break off the scale. Heavy acid treatment even HCl, muriatic acid, swimming pool acid (all the same stuff) will take forever to remove the scale. David