In my experience, the most likely cause for a plugged vent line is spider webs/nest or mud daubers having plugged the vent outlet. I work part time as a dockmaster at our municipal docks - which is one of the few pump outs in the area and sees a lot of traffic. We run into a lot of cases where the vents are plugged on boats that have not been used for a few weeks. The only cases I can recall of being unable to pump a tank were either plugged vents on the side of the boat, or the occasional owner of a vacuum head who does not turn off the vacuum pump (I understand there is no vent line in a vacu-flush head system).
Not likely to find dried "material" in the vent hose. Unless you REALLY overfill the tank there should normally only be liquid in the hose. The solid "material" settles to the bottom. Look at the vent fitting on the outside of your hull. It should have a piece of screen inside of it to prevent spiders and wasps from getting into the fitting. You will probably find mud or a mass of spiderweb material in the opening, and blocking the vent. Rick Brass Washington, NC From: CnC-List [mailto:cnc-list-boun...@cnc-list.com] On Behalf Of Jake Brodersen Sent: Sunday, November 03, 2013 9:29 AM To: cnc-list@cnc-list.com Subject: Re: Stus-List water level in head/bowl David, A leaking joker valve may allow the bowl level to rise over time. If your head is below the waterline, I suppose it's possible for some intake water to seep through the pump, but I've never seen that happen. Since you have closed the through hull, this is not the problem for you. As the level in the holding tank rises, it puts more pressure on the joker valve, which may cause it to leak more. If your vent is plugged, it may be better to replace than try to clean it. You could always try attaching a hose firmly to the vent hose. Just remove it from the through hull and seal it temporarily. It may not take much to clear it, depending on what is causing the clog. Dried material may need to soak before it clears out. Jake
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