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Old 04-25-2018, 10:23 AM   #1
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Pump-out troubleshooting

I have an ongoing problem with pump-outs only pulling one-half of the tank contents. Pumping out runs fine until about the half-tank point and then stops pulling. I cleared the tank vent line last season, but the problem recurred after two pump-outs. I am planning to clear the vent line again. This time I will rent a small compressor to make sure there will be enough pressure to clear any blockage.

I would like to confirm the vent line is clear before moving the boat to a pump-out station. The tank is a 25 gallon hard-sided plastic unit and is about three-quarters full. Here are some questions before I start the job:

1. Should I disconnect the vent line from the tank before pressurizing the line? Or pressurize the vent line while it's connected at the tank?

2. When I get the boat to the pump-out station, any potential problems if I pressurize the vent line from the exterior while pumping out?

and perhaps most important

3. Are there any other issues that could account for this scenario of pump-out failures? If there is a clog in the system, would the pump-out run ok and then always fail at the halfway point?

Thanks for any wisdom you can share.
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Old 04-25-2018, 10:30 AM   #2
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Open the pump-put BEFORE you pressurize the vent line, or you could cause a nasty explosion by pressurizing the whole tank
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Old 04-25-2018, 10:31 AM   #3
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Disconnect your vent line and then hook up a water hose to the vent on the tank side. Run and see if that clears your blockage. Then check the other side of the vent and the filter.
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Old 04-25-2018, 10:49 AM   #4
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Greetings,
Mr. ld. I had a problem earlier this year with just that. Only able to empty 1/2 the tank. Turns out the tube that went to the bottom of the tank internally had developed a hole in it's side and once the level of....um...effluent reached that hole, suction was lost.
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Old 04-25-2018, 11:22 AM   #5
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If you use a hand held, as opposed to a screw in, pump out simply lift it off when the flow stops. That will let air into the tank. Place it back on. If the flow resumes the vent is blocked.
It will flow until the vacuum in the tank overcomes the suction again.
Also you can hear the air rushing in around the pump out fitting.
Otherwise something isn't right with the fitting inside the tank. Some tanks have a tube to the bottom inside. Others just a low drain fitting outside.
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Old 04-25-2018, 11:58 AM   #6
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Thanks for the replies - all info noted.

This tank pulls from an outlet at the bottom of the tank - there is no dip tube.
I have pulled the pump-out fitting from the boat to let air in and that does restart the flow, but only for a very short time - then the flow stops again. There is something that happens at the halfway point. Still don't see what would cause this except a clogged or restricted vent line. So I will go ahead with servicing the vent line and see what happens.
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Old 04-25-2018, 12:00 PM   #7
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I would not recommend using compressed air to try and clear a vent line. Way too many potential problems and the consequences of those problems could be, uh, unpleasant.

Check where your pump-out hose is connected. If connected from the top, then consider what FF said about a problem with the pickup pipe going from the top of the tank to the bottom.

As ASD suggested, disconnect the vent line from the tank and check to see if it is clear that way. You don't really want to pressurize your holding tank.

I like Solly's idea as well.
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Old 04-25-2018, 12:36 PM   #8
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Quote:
Originally Posted by Solly View Post
If you use a hand held, as opposed to a screw in, pump out simply lift it off when the flow stops. That will let air into the tank. Place it back on. If the flow resumes the vent is blocked.
It will flow until the vacuum in the tank overcomes the suction again.
Also you can hear the air rushing in around the pump out fitting.
Otherwise something isn't right with the fitting inside the tank. Some tanks have a tube to the bottom inside. Others just a low drain fitting outside.
Great suggestion, had the same problem with hand held pump out, cleared vent and sucked it dry.
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Old 04-25-2018, 12:42 PM   #9
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How do you know the tank is still half full? Can you see the level through the holding tank walls?

I've fought with level senders in the past, as they tend to get sticky in a holding tank, and end up showing contents when there isn't. At least, mine have.

As to the vent, if it can pump halfway down with a clogged vent, with little air in there to start with, it should be able to pump the rest of the way down if you stop to let air in, resulting in a whole lot more air in there. Doesn't sound like a vent issue to me. It sounds more like something in the tank that clogs the opening once the level gets low enough. Might just be coincidental that it happens at around half full.

Edit: Thinking about it more, while eating lunch yet, if happens only when it's low enough to pull a vortex, it could be something floating on the surface that's getting pulled down to clog the suction line. Like a hollow plastic ball that got flushed. Had any little kids on the boat recently?

And I wouldn't pressurize that tank. Even a couple of psi on such large areas can cause large forces on surfaces not designed to handle it. Or blow a hose or fitting off the bottom, which may result in a Robin Williams in the RV movie dump station scene recreation.
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Old 04-25-2018, 01:05 PM   #10
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And remember that one aw sh#t outweighs 1000 atta boys in this situation.
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Old 04-25-2018, 01:11 PM   #11
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The tank's walls are translucent so the level can be seen.
Nope - no kids on board. It's possible there's something in the tank going back to the PO's time.

I'm going to blow out the vent hose after disconnecting it from the tank.
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Old 04-25-2018, 02:35 PM   #12
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Clean out the vent fitting on the tank while you have it off.

However, I don't think a blocked vent is the problem...if it were, the pumpout wouldn't be able get more than a gallon or two before the pump pulls a vacuum. I suspect there's something rolling around loose in the bottom of your tank that's getting pulled to the outlet fitting and blocking it. Fortunately too big to be pulled INTO the pumpout line, blocking it. If you never flush out your tank before winterizing, leaving sludge to harden into concrete, a big piece of it may have broken loose.

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Old 04-25-2018, 02:58 PM   #13
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Hello Peggy -- thank you for responding.
If there is something loose in the tank, are there remedies possible with the tank and hoses in place? Any products or techniques that might break up rogue solids? (fingers crossed, at this point)
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Old 04-25-2018, 03:56 PM   #14
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You might try Sew Clean Sew Clean It does an excellent job of cleaning the sea water mineral buildup out of piping. If your toilet uses fresh water, there's a product that's popular in the RV market that may work if Sew Clean doesn't...it's called Forget About It from a company called TankTechsRX TankTechsRX | Totally Green, Totally Clean! Keep in mind that either of these products may require multiple doses that may or may not have to sit a while.

Last resort may be to open (or install) the inspection port on the top of the tank so you can bring the pumpout hose onto the boat to stick it into the tank to finish pumping it out so you can see what's in it.

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Old 04-25-2018, 04:02 PM   #15
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Life was simpler in the 1960s. We spent most weekends sailboat racing in SF Bay. Doubt we ever pumped out a poop. And hardly a pee.
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Old 04-25-2018, 04:06 PM   #16
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Life was simpler in the 1960s.
Yes, but I would prefer not swimming in the head discharge.
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Old 04-25-2018, 06:40 PM   #17
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I had a similar problem on my current boat. It would pump fine for a while and then just stop. I finally figured out that the wye valve that switches between tank pump out and overboard discharge would switch itself under vacuum. It took me a while to figure it out, and I tried all the suggestions that you have gotten here first. So now I put a zip-tie on the valve when I am going to pump out. Problem solved .

Cheers, Bill
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Old 04-25-2018, 11:50 PM   #18
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Yes, but I would prefer not swimming in the head discharge.
Like"swimming undeterred"?
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Old 04-26-2018, 05:47 AM   #19
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On rare occasions some pumpout stations have weak vacuum. You might try a different pumpout.

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Old 04-29-2018, 01:19 PM   #20
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I rented a compressor and confirmed that the vent is clear.. I've done some research and followed up on Peggy's tips regarding Sew Clean and TankTechsRX. As Sew Clean is oriented towards saltwater systems, I chose to go to the TankTechsRX.com site and start reading. I have some experience with organic soils and how to husband beneficial bacterial populations in a new medium. The TankTechsRX products look like they're based on sound theory. I contacted the company and spoke with Don,the owner and founder, and discussed the scenario I'm dealing with. He agreed with Peggy's thoughts about the possibility of hardened sludge breakiing free from the tank walls or bottom and then blocking full extraction of the tank's contents.

So, I'm embarking on a test with this product. I'm quite confident that once the aerobic bacteria establish a "quorum" in the tank, they will liquefy the solids. The issue will be how long that process will take. Along with coaching from Don at TankTechsRX, I am going to introduce a 1/2 bottle of material into the tank through.the toilet. I'm going to introduce the other 1/2 bottle (mixed with water) down the pump out hose from the deck fill - so that two growing populations of beneficial aerobic bugs can work their through the sewage medium towards each other from both sides. Don said it will take about 3 days for the newly introduced bacteria to establish a colony and start to multiply. The plan now is to give the bugs at least a full week to do their thing and then try pumping out. It might take just the week or maybe a month - I'll find out. In the meantime, I'll be rooting for each of those little individual microbes to prosper and multiply and chomp chomp chomp away at their favorite food.

I'll follow up with results as they become available.
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