gray water tank double duty!

[oceane]

Hi Peggy,

i am at replacing the black (37gal) & grey(22gal) water tank. with the given space, it is difficult to increase the holding capacity.
Had in mind to connect both tanks in series so that if needed I could use the gray water tank as an overflow of the black water tank for increasing my holding capacity. I could connect plumbing to grey water tank to enable overboard discharge of showers and sink, when using the gray tank as an black overflow!!??

right now the gray tank is emptied via an internal sump pump. so i'm thinking of connecting both tanks to the macerator pump when using both as black, and still have an external sump with float swith for gray water mode!?

Is that doable?
any issues to consider?
what kind of valve to use to connect the black to grey tank in series, and avoid odor and blockage?

thanks "ahead " for your support

frank

 

[Calif. Ted]

Frank,
I think that once you use the gray tank for "black water" it's probably a black water tank forever, do you dispose of gray differently then black ? I'm not at all familiar with gray water tanks on boats but I don't see a distinction once both are comtaminated.

 

[Steve Dion]

What is the purpose of a gray water tank on a boat. This is typically dish washing discharge, and bathing (hands/shower).

The only place that I know about in my part of the country is Lake Tahoe where you cannot discharge your sinks/shower overboard. I realize that there are a few others in different parts of the country.

 

[Bill Roosa]

Plumbing check

If you only run the marcerator to the black water tank you will no doubt have blockages between the two tanks. The rate of draining when pumping out or marcereating is pretty high and you will need a fairly large diameter hose to accommodate the gravity flow of solids from the gray to the black tank.
Also, I'm thinking you have a gray water tank for some leagal reason so can you legally connect them this way?

 

[Peggie Hall HeadMistress]

I delayed posting an answer because...

Before I give him any advice, I need to find out whether he NEEDS a gray water tank...whether there's any new requirement to hold it in any British Columbian weaters. Have any of y'all noticed where he is? Way up an inlet that runs north off the Georgia Strait. And if he does, whether Canadian regs allow black and gray water to be combined in the same tank...USCG regs don't. They don't even allow any common plumbing because of the very real risk of e coli contamination of sinks and anything that might be around 'em in the event of a back up (though people do it anyway).

So tomorrow I try to contact Canadian CG in that area to find out what he needs to do. Stand by...

 

[Jalepeno]

Peggie,

http://www.env.gov.bc.ca/epd/epdpa/mpp/boat_sewage.html

The discharge restrictions are mainly for lakes, a few marine parks and some small harbours that don’t have a good tidal water exchange. I have never heard of a pleasure boat having a gray water tank and I don’t understand why he would be concerned about having a large holding tank unless he crosses the border into your waters, spend a lot of continuous time in one of the designated areas or is a live-aboard in a small harbour. Squamish and Howe Sound are not designated areas. There are very few pump-out facilities here and the only one I’ve ever been near is in Nanaimo Harbour. I have a holding tank on my sailboat but my guess is that only about ½ or a bit more of the resident pleasure boats have one. It is not mandatory on the British Columbia coast. I have never used a pump-out facility as my tank is usually emptied about mid way across the Strait of Georgia. We have a lot of water here with very few people.

If this sounds unpleasant, where do you think the millions of birds, fish, seals and whales go? Yes, some of our beaches have to be closed to swimming in the summer but it is not due to boaters, dogs or the city systems, the pollutions is caused by the resident Canada Geese that move to the grassy beach parks from our schools and golf courses. Most of the coastal smaller towns only have primary treatment (equivalent of macerator, settling and chlorine) and then everything goes into the ocean.

 

[Head Master18695]

Is it doable? Yes. Is it a good idea? No.

As has been stated earlier, in most areas it is OK to allow gray water to be discharged directly overboard. There are only a few land-locked lakes, or reservoirs, etc. where gray water must be held and may not be emptied into the water. Lake Champlain and Lake George (New York/Vermont) and Lake Tahoe (Calif./Nevada) are the only ones that I know of, for sure.

If the boat has an onboard sewage treatment plant, such as a Lectra/san or Purasan, DO NOT combine black water and gray water - the treatment unit cannot handle gray water, and will be effectively ruined. To my knowledge, there is no treatment system currently available on the market for pleasure boats, that can process gray water. It requires a completely different technology to that used for black water.

Pumpout and venting of the two tanks would also become a problem - they'd have to be joined both at top AND bottom, in order for the pumpout to work anywhere near properly - or each one would have to have its own separate pumpout system, defeating the purpose of joining them together. There are very few situations where two tanks are joined together on a boat, to increase the overall capacity, where it performs satisfactorily. Fresh water tanks - fine, no problem. Black and gray water tanks, nothing but problems. There is also an increased chance for the connecting piping to clog between the two tanks, where the passageways that join the two tanks together are limited in size, and more prone to clogging.

 

[Peggie Hall HeadMistress]

Thanks Jalapeno...that's the info I needed

And now I know what to recommend: get rid of the gray water tank and reroute your sink drains and any sump(s) to discharge directly overboard. That will free up plenty of room for a larger black water tank...which I don't think you need. Besides, maintaining a black water tank is a breeze compared to a gray water tank...you haven't known sludge and odor problems till you've dealt with gray water holding!

However, I can't imagine why you'd need more than 37 gallons of waste holding capacity. That's at least 60 flushes unless your toilet is a water and power hungry dinosaur (a problem that's actually easy to fix without breaking th bank)...60 flushes is enough for an entire week for a couple continuously aboard, required to hold full time...and you don't have to hold anywhere except for a few Provincial park anchorages.

So why DO you think you need a larger black water tank? What am I missing here?

 

[oceane]

many thanks to all for your advise and feedback....
the boat was purchased in Florida, and was used as a liveaboard at South Beach Yacht club....it came with a gray water tank set up for both showers!? but sinks are routed directly overboard!??

we are now refitting the boat to live aboard next year and go cruising afterward....being environment conscious (and i use to work for a biogas reactor cie!!..that would be a nice system if it could be downsized for a sailboat and run the methane gas thru your generator!!!), we like to hold as long as possible when spending extended time at same location , being at anchor or marina....in order to avoid having to discharge within the 3 miles zone...

given your advise, i believe i'll set up two independant black water tank, one for each toilet and avoid all the possible associated problem described. this way increasing holding capacity (37gallon hold us for +/- 10days) to 14+ days...
I did also look into a digester system like the Humphrey, but costly,more space involve and would still need to have a holding tank to avoid any discharge in some location.
are you recommending treatment system like lectrasan/purasan!???

to route the showers directly overboard seems to be a problem since drains are below waterline therefore would still need to be pumped....maybe i should just setup a very small gray tank to allow for just sump/pump overboard and not hold...?? or is there a easy way to have both showers drain connected to a direct pump system without any tankage!??

again, thanks for your support....

 

[Prime Time]

Better to pump your shower sump above the waterline

It is probably better to have your shower sump pumps discharge above the waterline via a thru hull.