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Old 10-07-2022, 07:49   #1
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Gray water holding tank

I have a gray water holding tank on my boat that all sinks, showers and appliances drain to. It has a float valve which operates a pump to drain it when itís full. I donít know how big it is, but guess maybe 10 gallons or so. The drain pump only ever gets it down to about half empty so thereís always quite a bit of water left in. None of the sinks etc have waste traps and so weíre having real problems with smells. Iím sure that itís because the tank never fully drains that we get stagnant water. Iíve read Peg Hallís excellent book and my next step is to try and figure out whether we have a proper tank vent and whether itís blocked but I have a more general question. Is the arrangement on my boat normal or is it just asking for problems. If I canít fully pump out the tank each time and smells can always come up via the sink or shower then unless I can keep the tank perfectly clean it feels like Iíll always have problems. The only thing that goes into the tank is sink and shower water; nothing from the black water system which is separate.
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Old 10-07-2022, 08:00   #2
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Re: Gray water holding tank

Welcome to CF

You haven't said were in the world you are, but first question is do you really need a grey water tank? I guess on an inland lake like Windermere it could be socially warranted, but in saltwater in the UK, probably not. A trip to Holland would also need close inspection of their rules for places like the inland meres.

Our sink and shower drain overboard above the waterline as do thousands of other yachts.

Pete

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Old 10-07-2022, 08:09   #3
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Re: Gray water holding tank

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Originally Posted by Pete7 View Post
Welcome to CF

You haven't said were in the world you are, but first question is do you really need a grey water tank? I guess on an inland lake like Windermere it could be socially warranted, but in saltwater in the UK, probably not. A trip to Holland would also need close inspection of their rules for places like the inland meres.

Our sink and shower drain overboard above the waterline as do thousands of other yachts.

Pete

In the sunny Solent
Funny that you should mention Holland, but thatís exactly where our boat was built. Weíre based in the sunny Solent, UK too although will be doing some inland waterway cruising. I have to say that I donít love the setup as I canít see how itís a good idea to have half full gray water tanks, but it would be a big hassle to re-route as we have 7 inlets to the tank.

The reason it only half empties is that the pump has a large inlet and starts sucking air when the tank is half full. I was think of attaching a 90 degree angle extension to the pump inlet so that it sucks water from the bottom of the tank and empties more of the water
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Old 10-07-2022, 08:46   #4
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Re: Grey water holding tank

Either way you are going to have to empty and clean that tank out, so why not solve the pick up problem at the same time . Since it was built in Holland that would explain the grey water system.

I think the sink one is probably the most important and perhaps doable without worrying about the rest. A simple two way diverter valve to an overboard drain above the waterline ought to be a days work. Even between the tides if you get all the ducks in order and fit most of it first.

Bits of food in the tank and grease is really going to create a bacterial soup and if you can't drain the bottom of the tank, oh lordy. You will need long marigold gloves.

That should improve life on board whilst being easy to switch for inland trips.

Pete
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Old 10-07-2022, 08:54   #5
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Gray water holding tank

Iíd think that adding pee traps just below each drain should solve the smell issue.
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Old 10-07-2022, 09:11   #6
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Re: Gray water holding tank

I also have a separate grey water tank where the shower and bathroom sink drains.I don't have a float switch. Just simply turn the pump on manually every time the shower is used. No pee traps and bad smells. But check the vent holes too. They get plagued very easily
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Old 10-07-2022, 13:43   #7
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Re: Grey water holding tank

I agree with everything Pete said, including Welcome aboard CF. And thanks for buying my book!

Gray water tanks are almost impossible to maintain. I don't know of any black tank products that are likely to do much about the odor because soap scum, body oils, cooking oils etc--even fat content in fish and meat that goes down the galley sink when you wash dishes-- create a "skin" on the surface that prevents the tank from "breathing" via the vent. Even the slightest motion of the boat disturbs the tank contents, sending odor up the drain...And btw, the LAST thing you want on a boat is p-traps in sink drains. All the stuff that creates the "skin" on the surface in the gray water tank builds up in the p-trap, eventually creating a clogged drain. Pete gave you the best and easiest solution.

The "fun" part will be cleaning out the tank after you've re-directed the plumbing to bypass it. The instructions in my book for cleaning the bilge should work if adapted a bit to use in a tank.

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Old 11-07-2022, 06:09   #8
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Re: Gray water holding tank

I think that this is changing and eventually all grey water will have to be processed and disposed of in an environmentally sensitive way


Bill (Lake Ontario for envronmental rules)



Our sink and shower drain overboard above the waterline as do thousands of other yachts.

Pete

In the sunny Solent[/QUOTE]
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Old 11-07-2022, 06:43   #9
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Re: Gray water holding tank

Not sure if you can get this product in the UK, but I highly recommend dumping about a quarter of a cup of Zaal Noflex Digestor in there - that stuff is amazing. Peg Hall recommends it for black tanks but I find it also works in my sink and shower drains.

Iím attaching a picture (hope you can see it) of a sink drain that I closed off and dumped a couple of tablespoons of Zaal in overnight. It spat up all this gunk and the pipe was so much cleaner.
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Old 11-07-2022, 06:44   #10
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Re: Gray water holding tank

Meant to say that it gets rid of all the smells too.
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Old 11-07-2022, 08:24   #11
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Re: Grey water holding tank

Quote:
Originally Posted by peghall View Post
"I don't know of any black tank products that are likely to do much about the odor because soap scum, body oils, cooking oils etc--even fat content in fish and meat that goes down the galley sink when you wash dishes-- create a "skin" on the surface that prevents the tank from "breathing" via the vent. Even the slightest movement of the boat disturbs the tank contents, sending odor up the drain"

--Peggie
There are several bacterial enzyme products (Amazon, eBay, etc)that actually "eat" the oils and organic matter. They eliminate the products in the tank that cause clogging and odor. Many of them are septic-safe cleaners.

I have two 20gal grey water tanks that all faucets and showers flow to and treat monthly via their respective drains. I have no smells, clean vents, and most importantly, no clogs or wear in the pump joker valves.

Green Goblin Drain Opening Packs
Oil Eater
Green Goblin
Prozyme Pro-Kleen liquid
Grease Eater and Grease Eater Turbo

Best of luck and fair winds.
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Old 11-07-2022, 09:33   #12
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Re: Gray water holding tank

Thanks everyone for all the helpful responses. Gives me a coupe of different things to try but I suspect a winter re-plumbing job will be where I end up. I actually cleaned the tank a few weeks back and it was in pretty good condition in terms of not having gunk on the walls etc. However, whilst it didnít look very bad, the water was certainly grey and pretty smelly.
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Old 11-07-2022, 09:48   #13
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Re: Gray water holding tank

Part of the reason for grey water tanks is to avoid more through hulls, Even if they are above the water line. Same as the reason for a sea jest for salt water inflow.
I just flip my grey water pump switch whenever i use my sink drain and the suction crates also helps drain the sink
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Old 18-07-2022, 21:34   #14
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Re: Grey water holding tank

Grey water holding tanks are more on the nose than black water due to the inorganic content such as surfactants. They are easily controlled though utilising some off the shelf products such as TankTechsRX, Forget About it for Boats and ProPower Grey Wastewater Tank Treatment. Both of these products are 100% natural and utilise microbial consumption rather than chemical masking of the problem.
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Old 20-07-2022, 13:17   #15
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Re: Gray water holding tank

Quote:
Originally Posted by Nickodemus View Post
Not sure if you can get this product in the UK, but I highly recommend dumping about a quarter of a cup of Zaal Noflex Digestor in there - that stuff is amazing. Peg Hall recommends it for black tanks but I find it also works in my sink and shower drains.

Iím attaching a picture (hope you can see it) of a sink drain that I closed off and dumped a couple of tablespoons of Zaal in overnight. It spat up all this gunk and the pipe was so much cleaner.
I'm looking for distributors in Caribbean UK or UE for Noflex sewage treatment.
should anyone be interested .Dist in the UK are only interested in heavy marine and don't care about retail (engineers what) Huge market in septic systems.
PM me if interested
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