Waste/Holding Tank Line Size ?

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mike0469
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Waste/Holding Tank Line Size ?

Post by mike0469 » Thu Aug 04, 2016 10:47 pm

Greetings everyone, I have gotten a lot of helpful information from this site since purchasing my F-36 late last year. I have been taking 1 week a month to do all my desired upgrades/repairs. I am down to the last thing on my list…the waste holding tank. My 1975 did not have a holding tank; however, I have moved things around under deck and have a new 50 gal tank. I have everything figured out, but have been questioning what seems to be an industry standard in regard to sanitary hose size. Everything I have read mentions 1-1/2" hoses from the electric toilets to the tank. Yet, almost all macerating toilets have a 1" discharge port w/1-1/2" adapter. Since great discussion has taken place regarding odors and the proper sanitation hoses, I am posing the following question:

Would it be better to use 1" sanitation hose for discharge all the way to the tank? I understand that simple logic dictates, the bigger the hose, the better, because it can't stop up easily. But I am thinking the smaller the hose, less water is required to flush the lines out after each flush to illuminate odors. This would save water with each flush. I am applying this thinking because of my experience in construction plumbing. I.E…a 3" drain line is better than a 4" line. The 4" line has a flatter bottom, thus, water will be shallow and waste/paper does not flow as fast. The tighter curve in the bottom of a 3" pipe forces waste to flow faster with the water.

If the macerator grinds the waste up enough to exit the 1" discharge, and the flush cycle is long enough to evacuate the line, would it not stand to reason the small line would be better. It would evacuate the line with half the water usage. There will be more resistance to the pump in the 1" line from the pipe walls; but there is more water weight resistance using the 1-1/2" line.

Just curious to get feedback from experienced minds on this before my boat becomes a lab rat!

Thanks.

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Big D
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Re: Waste/Holding Tank Line Size ?

Post by Big D » Fri Aug 05, 2016 6:50 am

Unless the plumbing from the toilet to the tank is downhill all the way, you will not "evacuate the line." As soon as the toilet's pump starts sucking air, it will no longer move waste through the line so whatever is left in the line will stay until the next flush. The larger line will of course require more water/cycles to fill with water in an effort to displace the waste. If you're worried about water usage, don't flush the line all the time, just use a really good quality line instead that doesn't permeate as quick. Where practical/possible in long runs and low lying areas that will always hold waste, you can use solid ABS which will never permeate.

The biggest worry for me would be the efficiency of the macerator in breaking up solids. It's efficiency is proportional to the buildup of waste/solids that will eventually build on the macerating hardware. If you're decision is to go with the smaller line, I would first ensure that the macerator is the blade type and not the type that looks like a plastic impeller with an attached back plate. I don't find that those chop up the solids effectively. Having said that, toilet paper will greatly diminish the efficiency of both types as the paper will wrap around the chopper blade/impeller. For this reason, I'd stick with the larger line. While the solids may start off leaving through a 1" port, will larger solids compact easier in the smaller line and be harder to move than in a larger line?

If you're doing a new tank installation, use a 1-1/2" line for the vent. Since marina pump-out machines and your pump-out line will be that size, the larger vent will allow for equalization so the tank won't collapse during a pump-out....very common issue with small vent lines like 5/8"
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prowlersfish
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Re: Waste/Holding Tank Line Size ?

Post by prowlersfish » Fri Aug 05, 2016 6:57 am

My Raitan has 1 1/2 discharge port it is a Macerator head . I looked on line and found the 1' is a option . I also found 1 1/2 seems to be the norm on the few other heads I checked . I would go with the 1 1/2 myself less restriction and less chance of plugging up .
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mike0469
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Re: Waste/Holding Tank Line Size ?

Post by mike0469 » Fri Aug 05, 2016 5:31 pm

Thank you guys for the input....1-1/2" it is ! FYI, I will be installing 2 - 1-1/2" vents; one on each side of the boat and at front and back of tank to get cross ventilation and to prevent collapse!

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Allen Sr
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Re: Waste/Holding Tank Line Size ?

Post by Allen Sr » Sat Aug 06, 2016 10:38 am

I would not use 1 1/2" line for your vent. I have a single 1/2" line for my vent and have no issues with tank collapsing. At 1 1/2" for vents you will never get your tank empty due to loss of suction from the super sized vents. If it was me I would run two 1/2" vents that should be plenty. Just my 2 cents worth.
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Re: Waste/Holding Tank Line Size ?

Post by prowlersfish » Sat Aug 06, 2016 11:31 am

Allen I will have to disagree , large vent hose will not cause a issue with pumping out . Your sucking from the bottom and the vents are on top .

While I don't see the need off 1.5" vent , it would not hurt .

IMO the best thing you can do for smell is to use fresh water from the boat to flush . ( along with treatment )
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jhalb
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Re: Waste/Holding Tank Line Size ?

Post by jhalb » Sun Aug 07, 2016 9:58 am

I would go with the smaller size and add a in line filter for your vent hose. This made all the difference with holding tank smell for me.
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Big D
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Re: Waste/Holding Tank Line Size ?

Post by Big D » Sun Aug 07, 2016 10:25 pm

I'll stick with my initial recommendation for a 1-1/2 vent. A lot of manufacturers are going that route now for a few reasons. Even the vent filters have the 1-1/2" option now. Absolutely no issues pumping out with that size vent, in fact it works better as you're letting in the volume you're displacing when being pumped out so it's way easier on your tank.
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Re: Waste/Holding Tank Line Size ?

Post by larryeddington » Mon Aug 08, 2016 11:17 am

If worried as I was about collapse you can purchase vacuum break screw on caps. I got a two inch one that fit in the clean out fitting I had put in. If my two 3/4 inch vent lines and charcoal filters should clog it will allow air to come in but nothing escapes. Probably overkill but they are not expensive. :D
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Big D
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Re: Waste/Holding Tank Line Size ?

Post by Big D » Mon Aug 08, 2016 9:53 pm

All kinds of fixes available out there after the fact but this is a new tank install so why not just install the larger line to begin with.
She was a 1969 36 ft wooden beauty with big blue 440s that we'll miss forever.
And thanks to the gang, 2012 Trojan Boater Of The Year

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