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Old 05-03-2005, 07:29 AM   #1
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1967 26' Overlander
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Portable Macerator Use

Last year while emptying out my Overlander in preparation for repairs, I came across a Macerator pump in a nifty carrying case. Basically, the pump is used by connecting it to the three-inch sewer outlet via the stinky slinky. The device then grinds up the solids & sends them through a garden hose into the sewer tap in the front yard. The PO was quite proud of acquiring the pump in ’69, and had great plans for it’s use. But he ended up never using it, and hence had no advice on it’s operation.

Now skip forward a mere 38 years to a week ago last Sunday. In getting the Overlander ready for our first trip of the season, I was faced with needing to empty the black tank before the 400 mile season opener because my four & five years old boys had repeatedly helped me test the new water pump installed a couple of weeks ago. Since I knew the tank had more than just water in it, the Macerator was returned to active duty.

Here’s the question: How much stretch should there be in the stinky slinky? Since getting rid of the tank’s solids requires that the liquid rush out of the tank as fast as possible, it would seem to me that the slinky should stretched as far as possible so as to hold as much as possible. But the 10 foot, 12 vdc power line on the pump will only allow so much.

The majority of threads I read on this subject were contributed to by people who had permanently mounted Macerators at the tank outlet, i.e. a low flow rate. I checked the output of the pump where it was draining into the sewer, and was impressed by the flow rate through a 5/8 inch garden hose, but I’m pretty sure it was not pumping as fast as it would have out of an open three inch hose.

Anyone have any advice or observations to share on the occasional use of a Macerator?

Thanks,
Tom
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Old 05-03-2005, 07:32 AM   #2
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advice

my advice is to never mix up that garden hose with your drinking water hose
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Old 05-03-2005, 08:03 AM   #3
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My guess is that it won't make any difference if you stretch out the stinky or not. In order for the tank to empty quickly, it needs to drain into a well vented container. In this case, the container (slinky) is not vented, the end is closed off by the pump. You will get an airlock.

Even if you have the pump turned on when you open the valve, the air cannot leave that much faster than the liquid would. You will get about a gallon of water quickly into the hose, then the airlock will slow the flow rate down to the 10 gpm that the pump can put out.

I think most people that use macerators have tank sprayers to help dislodge the solids that build up due to slower discharge rate.

My recommendation is, you will get slightly better initial flow with the slinky stretched out, but it won't help at the end of the process.
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Old 05-03-2005, 05:21 PM   #4
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Quote:
Originally Posted by markdoane
...Even if you have the pump turned on when you open the valve, the air cannot leave that much faster than the liquid would. You will get about a gallon of water quickly into the hose, ...
Excellent point Don. However...

At face value, I can't believe the pump, when running, is forming an almost hermetic seal keeping only a gallon or so of liquid from entering the hose. But I can't point to some text to substantiate my point of view.

It appears actual test data is in order.

Boyz ?!? Daddy needs to check out the the new water pump a bit more...

In the interim, I would like to hear if anyone else has additional test criteria!

Thanks Don,
Tom
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Old 05-03-2005, 06:38 PM   #5
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Quote:
Originally Posted by TomW
Excellent point Don. However...

At face value, I can't believe the pump, when running, is forming an almost hermetic seal keeping only a gallon or so of liquid from entering the hose. But I can't point to some text to substantiate my point of view.

Tom
Tom,

The seal won't prevent water from entering, it will just slow it down. To test this theory, put a glass over an open soda can and turn it over. You need to let the air out of the glass in order to let the liquid flow in.

In the same way, the air in the slinky has to get out of the slinky in order for liquid to flow in. Some of the air will work it's way back up the slinky, through the valve and into the tank. The rest will exit through the pump if the pump is running. Either way, the flow of liquid will be a lot slower than what you're hoping for.

I'm willing to say it won't be significantly faster than if you just hooked the macerator up directly to the tank. Using the slinky might be a little faster, but it won't get you the 'flushing' action you are looking for.

I'm willing to be proven wrong!

And I'm also interested in other opinions.
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Old 05-03-2005, 07:51 PM   #6
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Quote:
Originally Posted by TomW
......Anyone have any advice or observations to share on the occasional use of a Macerator?....
Tom:

For what it is worth, I do not feel as if anything is "left behind" with the use of a (relatively) low flow macerator...

I believe that the "solids" will sink, as solids are prone to do, do the "low point" of the system (the drain valve?), and the "solids" (or semi-solids) will be the first thing the macerator pumps - followed quickly by the rest of the "liquids" in the black tank (these liquids should push any residual solids to the pump), then flushed with the gray tank liquid.

I noticed in the pic that there is a water hose hooked up to the pump to pump out the grind and water - I think I would try to find a 1" or a bit larger hose for this use. At the same time, I think you would be better off minimizing the "upstream" length of the slinky. Otherwise, it looks like a great setup.

I can drain 60 gallons with mine in just a few minutes - and your pump appears to be more robust than mine is.

I use a 1 1/2" discharge hose, I believe the 1 1/2" is optimum to minimize line loss and provide a high enough velocity to move everything along.

I do not think you will have any trouble at all - just be sure that all "solids" have enough time to "liquify" prior to pumping - and, of course - make sure the "boyz" do not put anything the macerator cannot pump - if you know what I mean.
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