Is there an effective way to clear a blocked vent pipe for a holding tank?

[Nick in Manitou]

Robert,

That makes sense. If we are really getting the tank basically empty, then there is nothing to pursue...if not the dowel will tell us and then we know what we are facing.

Thanks!

Nick

 

[jmooney]

When the pumping starts and stops ,it is probably caused by the pump out system trying to build up enough vacuum. Try pumping out at high tide.

 

[Nick in Manitou]

Just to update this thread (in case anyone was wondering what has happened)...

It was suggested that I check the level of the material in the tank after pumping out in order to see if we were really getting everything out of the tank or if there was perhaps a dip-tube problem and a significant amount of material was remaining.

As suggested, I got a dowel and dipped the tank after the pump-out and only a few inches of stuff was remaining.

I also noted that inside the brass tee fitting where the pump-out hose attaches to the top of the tank, there is a PVC pipe heading down into the tank. I don't know if that is the result of a replacement of the original or if it was factory installed.

I should mention that we are on a floating dock, so when the pump-out folks come by, we are always the same distance above the dock.

A few of weeks ago when they came to pump-out the boat, the boss was along to train a new employee and when the system was appearing to start and stop, the boss had the pump-out line held against the vent fitting on the side of the boat. Perhaps that cleared a partial or intermittent blockage, I don't know but the last 2 pump outs have been without any problems.

So, I can't proclaim specific success of any particular method of repair, but at least for the moment, the problem SEEMS to have gone away.

Thanks for the suggestions and support,

Nick

 

[SKYCHENEY]

I think the PVC drop tube is original. My 1985 has that too. I don't know when they figured that out and switched to PVC but it appears it happened in the early 80's

 

[jmooney]

Unfortunately not in July 1983 . I set my new tube approximately 1 inch off the bottom of the tank. You mentioned you had several inches of fluid left after pump out. This seems to indicate that there still might be a problem.

 

[Nick in Manitou]

Jmooney, Thanks for your observation. I don't know how far above the bottom of the tank the current PVC tube stops, and I don't know if it is original.

Our boat is a 1984 and Sam's says that the records show it was delivered in January of 1986. So it sounds as though it might have been created during the transition to PVC...or the PVC might be a modification done by a previous owner.

The pump-out folks also pointed out that there is some amount of material in the hoses when they stop pumping that flows back down into the tank.

At this point, since the pump-out folks think the problem is fixed, I will go with that.

But your point is well taken. If the PVC is a repair that was done by a previous owner, how close to the bottom of the tank is it? If the 4 or 5" of material I saw on the dowel I dipped the tank with is significantly more than the distance of the PVC from the bottom of the tank, where did it all come from? - (A point to be made here is that the tank is sort of v-shaped with the narrow part (less than one foot wide) at the bottom, so a couple gallons at the bottom adds up much more quickly than further up in the tank.)

According to the documentation that came from Hatteras, the tank holds 105 gallons. Since we have it pumped every week and we are told that they usually get about 40 gallons out of it, as long as they (the pump-out folks) say that things seem to be working correctly, I think I will assume that we are in good shape.

Keeping an eye on things...

Nick

 

[Dazed338]

I had water drains on my decks get clogged up with 40 years worth of dirt and leaves etc. I did exactly what I told you to do with the hose left it on for about 30 seconds, I pulled the hose off and outcomes the clog and gunk for all those years now it’s free-flowing.

From time to time if mine get too bad use the pressure washer. Not sure I'd do that on a holding tank vent, might get a little shitty.

 

[Nick in Manitou]

Dazed338, I was concerned enough with just a small amount of pressure from the water hose from the dock pressed against the vent fitting!

 

[jmooney]

One quick way to see how far from the bottom the PVC pipe reaches , is to remove the plug on the tee and dip the tank with a coat hanger bent at ninety degrees at the bottom . After you touch the bottom of the tank, you can pull it up until it catches the bottom of the tube.

 

[ndow]

I had a similar problem with a Catalina sailboat I owned before getting our 40' Hatteras. Finding and fixing the problem was typical trouble shooting: Eliminate items 1 by 1 until you are left with the problem.

The problem was with either the pump out line or the vent hose. During a pump out, I created an air leak into the system. In my case, i had access to the plug on top of the tank that i could open. Any method of enabling air to get in will do. The pump out proceeded without any problems, so the pump line was clear and not the problem.

So on to the vent line. The most likely locations to clog are where the line connect to the tank as it can get clogged as 'stuff' sloshes around while underway. I was able to remove the vent line from the tank and inspect it - not the problem. I then turned my focus to the other end of the vent line that connects to the clam shell on the outside of the boat. I assumed a dirt dobber had done its deed and build a nest inside the clam shell, which is something I had experienced before. I was having a difficult time clearing it, so i got a Water Pik, with its 'hooked' tip and ran it up under the clam shell and let the water shoot into the vent - no luck. It is at this point that you start recognizing that you can't remove that clam shell fitting as it has a nut on the inside and it isn't accessible. So i drilled a hole in the outside of the clam shell and ran the drill down in the vent. A spider web pulled out and spun up on the drill bit. Tada, problem fixed. I tapped the hole and put a SS set screw in the hole to finish the job.

Hope that helps.

N. Dow

 

[Nick in Manitou]

Jmooney, Good idea. If I have to mess with this problem further, I will use your suggestion!

Ndow, On our boat, the vent lines from the holding tanks are round fittings that sit almost flush with the outside of the hull. I was able to use a hose to run some water from a hose on the dock into the system. The vent line has a 90° fitting bolted to the inside of the hull and the line rises up about a foot above the fitting before heading back down in what seems to be a continuous, winding slope to the holding tank. We did succeed in hearing water running into the holding tank while running water into the vent line from outside. I was ready to open the vent line at the tank if the pump-out folks had trouble the next time they visited, but they had no more trouble. Whether or not that means we were successful in clearing a blockage with the water hose running into the vent or with the pump-out fellow taking his vacuum hose to it is not something we have proven yet...but we have not had problems the last few pump-outs.

It would be nice to know exactly what the problem is/was and if we have actually removed the problem permanently, but at this point it seems to be working.

Nick

 

[Nick in Manitou]

PROBLEM SOLVED!

Recently changed pump out companies (again). The new company has a new boat with a new gasoline powered pump that has no problem at all emptying the tank in a fraction of the time the previous company would spend.

I have learned a lot about the holding tank system on this boat as a result of the issue the previous company had - but it is nice to know that the problem was not our system, but the pump out company's!

Thanks for all the suggestions...I will remember them!

Nick

 

[rwaldrop13]

I had a similar issue and ended up just running a new vent tube from the tank to the thru-hull. The only problem I ran into was PO used heater hose for the vent tube and it was so heavy and thick we had to cut it into pieces to remove it prior to running new tubing. That made for a fun project.