Yet another holding tank vent question...

AndyL

.
Jun 23, 2020
42
Hunter 36 Rock Hall
(These questions pertain to a 2004 Hunter 36 with a manual Jabsco head)

I recently started getting some back flow into my head. A few minutes after pumping, I hear air bubbles, then I get gradual back flow of water. I replaced a worn out joker valve with a new one and that didn't change anything. I am trying to make sure that my holding tank vent is not blocked and have a few questions about the vent.

- The vent exits out of the cockpit coaming(?) by the jib winch. The fitting has a central metal disc that appears to support a small mesh filter, so the actual hole is just a narrow ring around that central disc. Does that central disc come out so I can access the hole without this obstruction?

- It's not easy to get much water down through that deck fitting with a hose, but I did the best I could and water can be heard exiting the bottom of the vent tube and falling into the tank. Is that good enough to know the vent is OK?

- When I just completed a pump out, I could hear a pretty loud hissing sound of air being drawn into the vent. Is that normal or a sign that it may be partially clogged?

Thanks for your help.

Andy
 
Sep 25, 2008
6,315
Alden 50 Sarasota, Florida
Yes. Absent routine maintenance, it’s likely a boat that old will have a clogged vent. It should be easy to remove the vent cap for inspection and run a vacuum or (low) pressure air to it to determine how clogged it is.
 
Dec 2, 1997
8,129
- - LIttle Rock
Yep, you have a blocked--or at least partially blocked--tank vent. The two most common locations for a vent blockage are the vent thru--hull and the other end of vent line--that end of the hose and the vent fitting on the tank.

Hopefully you'll be able to remove that disc and screen in the vent thru-hull...don't worry about damaging 'em, you're not gonna put 'em back. Once you have an open thru-hull, put a hose nozzle against it and back flush the vent line. If you're lucky and have plenty of water pressure that may clean out the other end of the vent line without having to remove it from the tank to scrape out that end of it and the tank fitting. You can prevent future vent blockages by back flushing the vent line every time you wash the boat and/or pump out.

--Peggie
 
Oct 22, 2014
16,128
CAL 35 Cruiser moored EVERETT WA
Wow Andy. Brand new in the forum and you already hooked up with the Head Mistress. Could not be in better hands.
Welcome. Hope you resolve the stinky issue.
 

AndyL

.
Jun 23, 2020
42
Hunter 36 Rock Hall
Just FYI, when I eventually got the vent hose off, there was a blockage at the connector to the holding tank. I cleared it as best I could and put everything back together. Hopefully that helps.
 
Dec 2, 1997
8,129
- - LIttle Rock
Just FYI, when I eventually got the vent hose off, there was a blockage at the connector to the holding tank. I cleared it as best I could and put everything back together. Hopefully that helps.
That should help a lot 'cuz that blockage wasn't allowing any air to come in OR out of the vent. Did you also clean out the vent thru-hull? Better yet...replace it with an open "bulkhead" thru-hull that'll let you put a hose nozzle against it and backflush the vent line every time you wash the boat, which will prevent future vent blockages.

--Peggie
 

AndyL

.
Jun 23, 2020
42
Hunter 36 Rock Hall
Hi Peggie,

I removed the hose from the thru-hull, inspected it with a flashlight, and poked a zip tie through in multiple directions with no resistance. I hope that was enough to show it wasn't blocked. I know I should replace it as suggested and may try to do that next year.

Andy
 
Dec 2, 1997
8,129
- - LIttle Rock
removed the hose from the thru-hull, inspected it with a flashlight, and poked a zip tie through in multiple directions with no resistance.
Did you poked the zip tie through the vent line or the thru-hull? A screwdriver tip or an ice pick does the best job of cleaning out the vent thru-hull. And while you had the vent line off of it would have been the perfect time to swap the vent thru-hull for a bulkhead thru-hull...you obviously had access to it...you'd only have needed to break it loose from the bedding compound on the outside of the hull...sand smooth again...apply a little more bedding compound, insert the fitting, tighten the nut on the inside of the hull...done!

--Peggie