Flushing Vent Line

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Ed

I have a new boat (426 DS) and see a great advantage to keeping the holding tank in good shape. To that end it seems that a flush of the tank every few times it is pumped is in order and also to keep the vent line free a flush every now and then. My questions on flushing both of these items. Seems you should be able to fill the holding tank through the pump out fitting and it will vent through the vent line then pump the tank again. Unless I am missing something this sems straight forward -however, putting water down the vent line seems more complicated. I assume the pump out line runs to the bottom of the tank like a straw, so if I add water through the vent where will the displaced air vent? I have vacuflush heads so don't understand where the displaced air will go. What happens when you run water backwards into the tank through the vent line? Will it overflow out the pump out line? Thanks for any help here. Ed
 
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Bill O'Donovan

Simple enough

Someone on this site once recommended hosing water into the air vent while suctioning out the holding tank, clean out the vent line. The stuff goes back into the tank and out the suction hose. Don't make a big deal of it, just squirt a minute's worth to get the tank vent going in the other direction.
 
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Peggie Hall/HeadMistress

If the deck pumpout fitting is open

It will provide an escape for air in the tank displaced by water through the vent line. The rising water level in the tank will push air out wherever it can. Water won't overflow out the pumpout fitting unless the tank is overfilled. It's only when there's NO escape route for air displaced by tank contents that the tank pressurizes. However, Bill is right...just briefly blasting out the vent with a hose isn't likely to displace more air than can escape again once you stop. You might want to check out the link below.
 
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Terry

Hi Ed, Peggie and Bill's advice is right on...

Our 1991 P42 holding tank vent has the common clam shell shapped chrome scupper. In order to properly flush the vent line with each pump out I adapted a cone shaped garden hose spray nozzle with a piece of closed cell foam glued around the nozzle rim to act as a seal, which I place over the scupper. This way I know each time I pump out the system that the vent line is clear and clean. So, after I flush the tank until all that comes out is clear water I flush the vent line with my special nozzle followed by one last pump out. The previous owner unwittingly sold me the boat with a clogged vent line. The first clog I cleared was at the scupper, which was caused either by a critter nest or more likely backed up sewage. I thought that my vent clog problems would be cured by spraying the scupper after each pump out. Not so! The second clog happened later. It was at the bronze vent elbow on the tank, which became clogged from hardened gunk. I used a bent wire coat hanger to break the stuff loose. With my latest invention I know with each pump out that my vent line is clear because I can feel and hear the water flow through the line into the tank. Just spraying the scupper alone is not enough. Terry
 
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