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Old 09-19-2013, 10:09 AM   #1
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Holding Tank filter

I've alway thought $100 for a holding tank filter was high for a peice of PVC, end fittings and some charcoal. So I cut one open, put a coupling on it and refilled it with charcoal. One side of the coupling is not glued so it can be refilled. Charcoal, which I only used a third was $15 and the coupling was $1.50. It will cost me abot $5 from here on out.
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Old 09-19-2013, 10:17 AM   #2
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Nice work but the reality is a holding tank should never need a filter. It should never smell. The reason a tank smells is because there is not enough ventilation for the microbes to do their thing. Builders never put in large enough vents. A holding tank should have two good sized vents for cross ventilation. Adding an external ventilator is a good choice if adding a second vent is impossible or significantly increasing the size of the exiting vent isn't doable either.
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Old 09-19-2013, 10:18 AM   #3
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Quote:
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I've alway thought $100 for a holding tank filter was high for a peice of PVC, end fittings and some charcoal.
interesting post but I wonder if a filter is even necessary..
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Old 09-19-2013, 11:45 AM   #4
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Trust me when I say that it definitely is necessary. I did a "customization" of my filter like fryedaze did on his, and you can definitely tell when the charcoal needs to be changed.
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Old 09-19-2013, 12:15 PM   #5
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It should never smell. The reason a tank smells is because there is not enough ventilation for the microbes to do their thing. Builders never put in large enough vents. A holding tank should have two good sized vents for cross ventilation. Adding an external ventilator is a good choice if adding a second vent is impossible or significantly increasing the size of the exiting vent isn't doable either.
I have read a little on this forum about ventilation needs for holding tanks and I just cant see the rules of normal sewage treatment applying to boat holding tanks that may be pumped out as frequently as weekly. I just dont see the digestive environment being set up in the tank if you keep removing the waste.
I could be way off base and have no real basis for my theory. I am sure the Head Mistress could straighten me out.

I am not at Sanitary Engineer and never played one on TV.
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Old 09-19-2013, 12:43 PM   #6
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I know Peggie Hall doesn't like filters in the vent line. She doesn't want to restrict the air flow and she says they often get blocked.

I'm not sure it's possible for the typical 5/8" ID vent line to supply enough air to support the aerobic bacteria any way. Maybe the filter is the way to go. Let it stink, pump out often, and change the charcoal.

Another way to go would be Groco's Sweet Tank Kit. It pumps air into the bottom of the holding tank whick kills the stinky bacteria.
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Old 09-19-2013, 01:10 PM   #7
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Anerobic bacteria grow in oxygen deprived areas. Arobic bacteria grow in areas of plentiful oxygen. Anerobic bacteria produce the sulfides usually associated with the sewage smell. Aerobic bacteria eat the anerobic bacteria thus eliminating the odor. Ventilation equals a happy tank and raft up partners.
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Old 09-19-2013, 02:32 PM   #8
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Hi Don, you're exactly right. The problem is how do you get enough air into the tank to encourage the aerobic bacteria. There is no reason for air to naturally flow through a small vent hose. In fact since the anaerobic guys are producing various gases it seems to me there would be a steady flow of stinky gas out the vent and no chance for clean air to come in.

A couple of huge vents might get an exchange of air into the tank but that's hard to do.

I think you would need to mechanically ventilate the tank. You could use a small fan or an air pump like the Groco Sweet Tank uses.

The other option is to deal with filters in the vent line and live with the anaerobic bacteria.
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Old 09-19-2013, 02:42 PM   #9
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My home made Holding tank aerator using a bait 12v air pump & stones. It works well, I still have to do some work on the vent line it has some low spots that collect water, also the vent fitting, needs replacing it is too small and wasps, spiders, etc block it.
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Old 09-19-2013, 06:20 PM   #10
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Quote:
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I know Peggie Hall doesn't like filters in the vent line. She doesn't want to restrict the air flow and she says they often get blocked.
I'm glad to hear the Peggy is opposed to filters in the tank. I think that lady knows what she's talking about.

My boat has 2 vents for the holding tank and a clogged filter which I am going to remove. I'm also an advocate of venting the tank as much as possible. (Thanks, AL.)
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Old 09-19-2013, 08:30 PM   #11
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Steve, Nice job. Did you just use aquarium air stones and pump?
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Old 09-19-2013, 08:51 PM   #12
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What would your thoughts be on a Lil' Stanker RV Vent Fan from

www.lslproducts.net
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Old 09-19-2013, 09:39 PM   #13
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What would your thoughts be on a Lil' Stanker RV Vent Fan from

www.lslproducts.net
It seems that two vents would be needed depending of whether you used the fan for a puller or pusher. I don't see why it couldn't work. Don't know if it would be rated for use in a gasoline powered boat.
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Old 09-19-2013, 11:28 PM   #14
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Quote:
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Nice work but the reality is a holding tank should never need a filter. It should never smell. The reason a tank smells is because there is not enough ventilation for the microbes to do their thing. Builders never put in large enough vents. A holding tank should have two good sized vents for cross ventilation. Adding an external ventilator is a good choice if adding a second vent is impossible or significantly increasing the size of the exiting vent isn't doable either.
Aren't you guys beating this dead horse?
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Old 09-20-2013, 08:38 AM   #15
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I understand the theories but practice is something else!! No way to simply get air down to our tank. Had enough trouble with air pumps and air stones in our big fish tanks! Tried the charcoal in a similar (bigger) home made filter housing (4inch PVC). Helped a bit but still got stink on flushing. Just switched to RV holding tank blue chemical additive. Problem solved. I am not trying to encourage good bacteria. I am trying to kill all the little suckers - good and bad alike!! If it works for RV's on land, why not floating RV's?
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Old 09-20-2013, 10:29 AM   #16
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I understand the theories but practice is something else!!
It's not all that bad ...

The rate at which bacteria digest sewage in a holding tank is remarkable. If you supply a source of aeration and mixing (aeration can be enough to provide that) then the aerobic bacteria will make short work of the nasty stuff that makes bad smells.

The latest and greatest marine systems use aeration and specially bred bacteria to very rapidly decompose organic material so that nanofilters can remove the remaining solids and discharge near drinking water quality effluent.

A small blower or compressed air source or a recirc pump with a venturi to admit air will provide adequate aeration for a small holding tank. You can purchase bacteria from a number of sources.

The small boat (<50') world is still in the dark ages with respect to onboard sewage treatment and the boating stores only promote and sell the same old stuff they had 20 years ago.
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Old 09-20-2013, 11:02 AM   #17
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Wow, all I wanted to do was share my cheapo way of changing out the charcoal. Always learning here on TF.
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Old 09-20-2013, 11:04 AM   #18
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Wow, all I wanted to do was share my cheapo way of changing out the charcoal.
Ya done good.
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Old 09-20-2013, 02:38 PM   #19
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Steve, Nice job. Did you just use aquarium air stones and pump?
No the pump runs off of the boats 12V system. the pump and the stones are shown here;
Marine Metal Products Power Bubbles : Cabela's

This is available at many sporting goods stores, made to aerate a 15 gal minnow tank seems to work fine for the holding tank the stones have not clogged the pum runs all the time while out on the water 60-90 days/year. There are other bubbler attachments instead of the stones one like a small plastic ring with many small holes I have one but haven't tried it.
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Old 09-20-2013, 10:50 PM   #20
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Steve,
The bubbler looks like the answer to holding tank oders. As our holding tank is under our aft bunk I'm wondering how noisy the pump is. Would it be suitable in such an application or would it have to be mounted remotely?
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