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Old 18-06-2016, 09:24   #1
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Strong Back Pressure in the Head, Part II

I was following this previous “Strong Back Pressure in Head” thread as we happened to have the same issue just recently and are actively trying to solve it. That thread appeared to solve the original posters problem then seemed to change into a bunch of posts where other posters shared their experiences with toilet issues. My problem appears to be almost identical, but unfortunately I don’t think it is going to be as easy as replacing the pump. I hope I am wrong.

First, a quick question for Peghall, I tried to follow the instructions for your test from your post on the other Backpressure thread, but had a question. I disconnected the discharge hose from the pump (when I did this pressure was released). The flush water inlet and all other connections were connected. At this point you said to see if it “works” in both dry and wet mode. In both dry and wet mode I could pump without backpressure. In wet mode as soon as the flush water enters the bowl above a certain level it slowly drains out of the discharge connection on the pump because the flapper valve (not sure if that is the official name) doesn’t prevent water in the bowl from coming out. So by “see if it works” do you mean being able to pump it without back pressure? Or something else?

First our setup: We have the Jabsco manual pump toilet that pumps directly into the top of our holding tank through the discharge hose. From the bottom of the tank the waste goes directly into a hose that goes down to a seacock for discharge overboard or there is a pump out deck access. It is vented and the vent is NOT clogged. I’ve checked that and even did all of my experiments with the pumpout deck access open just in case.

Here is what we are experiencing: We are the original owners and have never put anything into the toilet that we didn’t eat ourselves. We are strict about that. After using the head and pumping several times the pump began to “push back”, meaning there was backpressure causing the pump handle to be increasingly difficult to pump. There was enough pressure that after forcefully pumping against the backpressure in hopes that it would push through, it actually inverted the joker valve. We then replaced the joker valve. Not surprisingly this didn’t solve the problem, but needed to be done. Next we replaced the pump with an older pump that we had replaced last year and kept around as a spare (we usually replace the pumps annually). Still experiencing backpressure after about 3-5 pumps. Next up, we used a 5 meter snake and actually snaked the full 5 meters. This head has a long discharge hose to the tank so I’m not sure exactly how long it is. Plus it is extremely difficult to replace. We just finished snaking it and are still getting back pressure. Nothing so far has worked.

What is is definitely NOT: Please don’t post saying you fixed your problem with any of these issues, as I have checked and double checked these and it is not the cause of our problems: all seacocks are open, the wet/dry valve is being pushed all the way to one side or the other, the vent is not blocked, I repeat, the vent is not blocked, any suggestions to “put X or Y into the toilet and pump it through” is not helpful because I cannot pump anything through because of the backpressure.

We’re stumped. We are hoping that despite everything pointing to a blockage in the hose, it is something else that is easier to fix. The only thing we can think of is that maybe the hose is just longer than 5 meters and the snake pushed the blockage close to the top of the tank, but not fully through. Really at a loss here. Any ideas?
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Old 18-06-2016, 09:44   #2
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Re: Strong Back Pressure in the Head, Part II

I assume you snaked it from the toilet side. Take the hose off of the top of the tank and pour water from that end to see if it is still clogged, or maybe try the snake from that end.



Any low spots in the hose will form a concrete hard mass of waste. Lots of threads on doing lots of pumping and using vinegar once a month to prevent. When I redid my system the hose I took out was 3/4 full of concrete.
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Old 18-06-2016, 11:06   #3
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Re: Strong Back Pressure in the Head, Part II

..So by “see if it works” do you mean being able to pump it without back pressure?

Being able to pump the toilet in both modes without backpressure. If you can't, the problem isn't in the toilet, it's somewhere downstream of the toilet, either a blockage in the toilet discharge line or a blocked holding tank vent.


In both dry and wet mode I could pump without backpressure. In wet mode as soon as the flush water enters the bowl above a certain level it slowly drains out of the discharge connection on the pump because the flapper valve (not sure if that is the official name) doesn’t prevent water in the bowl from coming out.


The pump works the same way in either mode, the only thing that switching to "dry" does is move a little "gate" into place to block the flow of flush water. So when pumping the toilet in the dry mode, the pump should push water out of the bowl at the same rate the pump pulls it into the bowl and pushes it out in the wet mode...UNLESS you were pumping it without the joker valve installed. Without it,the pump can't create the vacuum on the upstroke needed to create the pressure on the downstroke needed to push bowl contents out (which, btw, is why it's so important to replace the joker valve in a manual toilet at least annually).

You're adamant that the tank vent isn't blocked, but unless you've filled the tank with enough water to overflow out the vent and seen it POUR out, not just dribble, I'm not convinced, 'cuz opening the deck pumpout cap isn't a reliable test...it just prevents a strong pumpout from pulling a vacuum. And snaking the entire toilet discharge line pretty much rules out a blockage in it. The tank vent seems to be the only thing left...and as Sherlock Holmes observed, when you have eliminated every other possibility, what's left--no matter how improbable or even impossible it may seem--MUST be the answer.

The two most common locations for a tank vent blockage are the thru-hull and the other end of the vent line...that end of the hose and the tank vent fitting. While there's no pressure in the system, use a screwdriver blade, ice pick or whatever works to clean out the thru-hull...if there's a screen in it, remove it...screens cause more problems than they prevent. Then remove the vent line from the tank and scrape out what you find in the end of the hose and the tank fitting.

I'd bet real money that'll solve your problem....or at least I would have till I read Cal40Jon's reply. He could be onto something. An easier way to find out than snaking again from the tank end of the hose might be to remove it from the tank and stick it into a bucket, then pump the toilet in the wet mode--after you've put it back together!--to see if the water makes it to the bucket. If it does, it HAS to be the tank vent!
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Old 18-06-2016, 11:09   #4
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Re: Strong Back Pressure in the Head, Part II

test whether blockage is before the header tank or after by removing deck pump out screw and then pump. if it's ok then blockage is in line from tank to thru hull.
the only time I had this roblem is when I serviced the valves and put the pump unit top back with the flush lever in the wrong position.
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Old 19-06-2016, 10:14   #5
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Re: Strong Back Pressure in the Head, Part II

So there is a good chance I am going to have to eat my words on this one. After Peghall’s post that her money was on a blocked vent despite my insistence otherwise, we got up early before leaving the dock this morning and filled the holding tank (which was empty) with fresh water. As we expected water came rushing out of the vent no problem. Feeling vindicated we even took a picture to share. Fast forward about mid-day, while sailing along we emptied the tank (which was still full of fresh water). A little bit later out of curiosity we pumped the toilet and there was no pressure. It officially works! Since the vent did not appear to be clogged or blocked, I’m not positive that was the issue, however we did nothing else to it after our original post. Possibly after snaking it we somehow moved things around so that the water in the line could dissolve any “matter” over night. Not sure. Still hesitant to truly put it to the test, but the backpressure issue is officially gone. Thank you Peghall and everyone else, for your input, it is always appreciated.
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Old 19-06-2016, 10:27   #6
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Re: Strong Back Pressure in the Head, Part II

Just saw this post and I've had the same issue with our head a couple of times. What seems to happen is the dry/wet bowl leaver will stick part way between wet/dry. If we push it all the way to dry everything works. I've tried rebuilding but cheapest and simplest seems to be to replace the pump assembly and then good for another 4 to 5 years.
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Old 19-06-2016, 11:21   #7
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Re: Strong Back Pressure in the Head, Part II

I've had this same problem twice with my Raritan.
Each time it turned out to be a blockage on the intake side, specifically at the intake screen. Each time the screen looked clean. The culprit both times was a small fish had gotten itself jammed at the intake side inlet of the screen. It was jammed on the intake side, inside the plastic hose barb that is part of the intake screen housing. Even when I took the screen out I could not see the fish. Each time it would still allow water to get past the fish, bringing water into the toilet bowl, which made me think it was the outflow side of the toilet, or the vent. But each time it was a small fish. The first time I took the entire pump apart, put in a rebuild kit, snaked the hoses and cleaned the vent, all to no avail, until I found the fish. The second time it occurred I went straight to the screen housing and found another fish. My Raritan had exactly the same symptoms you described.
The little buggers back into the intake and when you start flushing it draws them into the screen housing, they stick out their fins and jam themselves inside the intake hose barb. The first one came out in pieces because I used a pair of needle-nose pliers to pull him out by the tail on the screen side. The second one came out still alive and kicking, because I took the hose off of the barb. Next time I'll take photos as proof.
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