Peggy - our holding tank has 4 holes - three large and one small. The small one is plugged, the large ones go to - 2" pump out on deck, 2" head outflow and 2" electric discharge pump. So either my tank is vent free or the pump out pipe does double duty or the plugged 1" hole should be conenected up. (This may explain my previous posting of bubbles coming out of the 4" inspection port when I pump out the head to the holding tank). My wife bought a head filter kit - it is expensive - is it necessary? Where do we put it ?
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The small line is the vent...unplug it
Pumpout pipe cannot do double duty...the tank must have a vent line running to the outside of the boat...because...The tank vent serves two functions: 1. Air in the tank that's displaced by incoming waste has to be able to escape out the vent...if it can't the tank will become pressurized, forcing air--and also waste that's now under pressure--to escape wherever it can...out the inspection port, back up the hose into the toilet, or even out the crack that enough pressure can cause to happen in the tank. 2. There must be a source (the vent) of incoming air to replace tank contents as they're pulled out by the pumpout or macerator. Without it, the pump will pull a vacuum that prevents anything from being pulled out of the tank, and can also crack your tank. And btw, ALL tanks--fuel and water too--must be vented for the same reason. If your water and fuel tanks aren't vented, or the vent becomes blocked, you wouldn't be able to fill 'em...you would get a little bit out before the fuel pump or water pump pulls a vacuum. So you need to unplug the vent fitting on the tank and run a line from it to an above-waterline thru-hull that's high enough to stay out of the water when the boat is heeled. As for where the vent filter goes: back to the store. As you've noted they're expensive...only last a season at most...and are toast immediately if they get wet--which is highly likely to happen when your boat heels enough to spill tank contents into the vent line. Worse yet, filters actually help to create the problem they're sold to solve...they trap noxious gasses, but the block the free flow of air through the vent line needed to prevent the noxious gasses from occurring. And btw, unless the rest of your sanitation plumbing is as weird as the tank vent situation, the hoses are actually 1.5" and 5/8"...hose sizes are always determined by the INNER diameter, never the outer diameter. I think the link below would help you a LOT when it comes to understanding how a sanitation system is supposed to work, how to maintain it to PREVENT problems, what causes odor and how to elimnate it.
Pumpout pipe cannot do double duty...the tank must have a vent line running to the outside of the boat...because...The tank vent serves two functions: 1. Air in the tank that's displaced by incoming waste has to be able to escape out the vent...if it can't the tank will become pressurized, forcing air--and also waste that's now under pressure--to escape wherever it can...out the inspection port, back up the hose into the toilet, or even out the crack that enough pressure can cause to happen in the tank. 2. There must be a source (the vent) of incoming air to replace tank contents as they're pulled out by the pumpout or macerator. Without it, the pump will pull a vacuum that prevents anything from being pulled out of the tank, and can also crack your tank. And btw, ALL tanks--fuel and water too--must be vented for the same reason. If your water and fuel tanks aren't vented, or the vent becomes blocked, you wouldn't be able to fill 'em...you would get a little bit out before the fuel pump or water pump pulls a vacuum. So you need to unplug the vent fitting on the tank and run a line from it to an above-waterline thru-hull that's high enough to stay out of the water when the boat is heeled. As for where the vent filter goes: back to the store. As you've noted they're expensive...only last a season at most...and are toast immediately if they get wet--which is highly likely to happen when your boat heels enough to spill tank contents into the vent line. Worse yet, filters actually help to create the problem they're sold to solve...they trap noxious gasses, but the block the free flow of air through the vent line needed to prevent the noxious gasses from occurring. And btw, unless the rest of your sanitation plumbing is as weird as the tank vent situation, the hoses are actually 1.5" and 5/8"...hose sizes are always determined by the INNER diameter, never the outer diameter. I think the link below would help you a LOT when it comes to understanding how a sanitation system is supposed to work, how to maintain it to PREVENT problems, what causes odor and how to elimnate it.
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