Analysis and Design
When sanitation system odors end up on the wrong side of the hoses and tanks that are designed to contain them, the most frequent analysis is, “they are permeated” and a lot of the experts call for wholesale hose replacement. In fact, while this may ultimately be necessary, it’s often a case of addressing the symptom rather than the cause. If the hoses are replaced and the design is flawed, then it’s likely the new hoses will, once again, fail or permeate prematurely. (see avoiding sanitation woes)
How do you test for permeated hose? Once you have eliminated all other sources for the odour, take a flannel and soak it in hot water. Ring it out and drape over the suspect hose for a few minutes. Then take the flannel and place in a zip lock bag and take outside to fresh air. Open the zip lock bag and smell. If you smell sewage, then you hose is permeated.
Before I begin with my solution(s), I just want to recap some of the salient points for a healthy head/holding tank systems and things you should look at on your boats sanitation system. By ensuring these procedures and implementing the points below on design layout, they can greatly reduce the the permeated hose problem.
- Rinse the holding tank out before layup and after every pump out. Lots of H2O helps with cleaning the remainder of the "solids" which tend to fall to the bottom of the tank and build up.
- If the holding tank has an inspection port, use that to wash down the sides of the tank; but watch for splatter back!!
- What sort of tank should I have? I prefer polyethylene tanks. The holding tank in many boats is constructed of low density polyethylene, heat welded from flat sheet with polyethylene fittings. Not much can go wrong as polyethylene does not corrode, is impervious to odour and has great impact resistance. Fiberglass would be my second choice. Metal tanks are a poor choice due to corrosion.
- Next step is to check the other components, Y valve, macerator pump, hoses, hose clamps, tightness of joints, and vent line. Two outlets can prevent the need for a Y valve.
- Flow into the tank from the head should be on top of the tank This will depend on your location of the tank, but if attached to the side, slosh from a boat heeling can back flow down the delivery hose and becomes the standing waste inside the hose. It also allows you to disconnect the hoses from the fittings if the tank is near full
- The air vent should also be at the top of the tank and as large as practicably possible. Better still, put two vent hoses on to allow for a cross flow of air inside the tank. Aerobic bugs don't make the stink. Anaerobic bugs are responsible for the sewer smell.
- The discharge line should also come from the top of the tank with a drop pipe. It is a poor design when the discharge is from a fitting at the bottom, or lower side of the tank and this leads to the hoses continuously submerged in effluent.
- All hoses should run "down hill" or free draining to prevent standing effluent. When hoses are installed with large dips, low spots, or "u" shaped bends, effluent will settle in those bends, and it will be a challenge for even the best permeation resistant sanitation hose. These low spots can also lead to clogging.
- From the Macerator pump, it pumps up hill to the tank and if not flushed sufficiently, effluent stays in the line.
- The intake to the holding tank is on the side and should be on the top
- The outflow from the tank is from the bottom and therefore effluent will sit in the hose from the outlet to the Diaphragm Pump. A better option would be to have the outlet from the top of the holding tank with a drop pipe inside to the bottom for pick up
|Barrel connector = big Nut|
I also acknowledge that if you are using sanitation hose with barrel connectors each end, that they then in turn have to be connected to your devices. If your devices don't have a screw in fitting (like most PE holding tanks do),and has hose tails only, then one is faced with extra hose and hose clamps at each end. I think this is worth the extra "risk", and if the hose tail off the barrel connector is kept close to (<1/8 inch) from your device hose tail, then permeation at those points would be minimal.
Below are some photo's showing the ease of the barrel nut disconnect, using both sanitation hose (in white) and Alkathene (MDPE) pipe in black.
You can place the nut of the barrel nut so that either stays on the removed hose section, or stays at the appliance fitting end.