The white Trident 102 hose is good hose, easy to work with and does not pass odor. Don't underestimate the "easy-to-work-with" part of the equation, most other hose rated for holding tanks does not flex well and is difficult to fit over barb fittings. Shields does make a super expensive lifetime warranty hose called Poly-X, its $25 or $30 a foot. I used a one foot piece to connect my head outlet to the rigid PVC pipe drain for two reasons. One, it mated to the hose barb connection on the bonze fitting on the head outlet and Two, it was going to be filled with fluid 24/7 because the head was about two feel lower than the top of the holding tank. No way around that geometry so I used the best stuff I could get. It was good to work with and zero problems for the past 10 years.
Use solid PVC pipe wherever you can, especially wherever your tank product is sitting inside the tube. You can't make the vents too big. Plastic-Mart will make a custom tank, any shape and size, connections whatever size wherever you want. Well placed vents only smell if you fill the lines with stuff. A well ventilated tank won't smell. Two vents are double plus good.
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You can use these for thru hull vents, no screens is fine but check them regularly for mud dauber wasp nests as they will clog up the vent and make them not vent.
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All the advice about downhill is important but difficult to do. Do your best and redouble your efforts to put in a dedicated fresh water flush tank, makes all the difference in the world. It is more expensive to put in a drain with a valve as shown below but it helps when you have to, eventually, remove the tank. It gives you a means to flush it out and plug it shut before you drag it out of the boat.
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