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Old 03-23-2018, 01:07 PM   #1
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Holding tank question

Just installed a new 40 gal. holding tank from Ronco under the floor of the forward companion way. The tank is 14” wide 12” deep and 60” long. There’s two 1” openings on the top of the tank. One at each end. One is routed about 6’ to the side of the boat.
Routing the second vent to the other side of the boat would require about 12’ of hose. So here’s the question.
Am I better off with a 12’ run with a couple of turns for the second vent, or would I be better off to pump fresh air into the tank( via some sort of small 12 volt air pump) like the Groco sweet tank system?
Next question is this. If natural ventilation will provide enough oxygen to keep the contents in the tank aerobic , why can’t I pump a small continuous flow of air into the tank at one end and vent the tank at the other end and achieve the same results? I know the Groco system uses a bubbler in the bottom of the tank that looks to be about 6” long. I can’t see how that’s going to help in a tank 60” long. Am I missing something or??? Thoughts and suggestions appreciated.

Don
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Old 03-23-2018, 01:21 PM   #2
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With a 1" vent you should be fine even with a 12' run. Most vents are 3/4". Make sure you have no dips- all uphill.

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Old 03-23-2018, 05:10 PM   #3
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Quote:
Originally Posted by djmarchand View Post
With a 1" vent you should be fine even with a 12' run. Most vents are 3/4". Make sure you have no dips- all uphill.

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Old 03-23-2018, 05:54 PM   #4
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The vent hose is 1". Are the vent opening in the hull 1" as well?
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Old 03-23-2018, 07:53 PM   #5
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The vent thru hulls are 1” Forespar Marelon mushroom head . (Non metal)
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Old 03-23-2018, 08:18 PM   #6
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My new vents will be 1.5". One will be near the bow, to replace and existing one and the other will be right beside the tank. While under way, there will be a higher pressure at the bow and lower at the side so there should be a flow through the tank. At anchor, if allowed to swing with the wind, same thing. At a dock, you could use a small fan to encourage the flow but that's probably a waste (not a pun) of time; not sure if 1" is enough even though it is very common but most tanks only have one vent so its 100% better than most. Just don't succomb to the lure of the vent filter, big mistake.
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Old 03-23-2018, 08:58 PM   #7
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Sounds like a good plan. I have one vent plumbed straight out the side of the boat. I might run the second vent line to the forward bow area on the opposite side of the boat as you suggested and see how it works. It would probably be about 10 ‘ of hose running uphill from the tank to the thru Hull.
If that works it would be a simpler solution versus the Groco Sweet Tank system.
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Old 03-24-2018, 07:20 AM   #8
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They are not robust enough to step on , but the RV folks have vents that are shaped to create suction to vent a tank when a breeze blows past.

https://www.amazon.com/Camco-40595-W.../dp/B003P64XU4
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