{Stus-List} Mr. Wizard Question re: holding tank venting

Indigo indigo at thethomsons.us
Sun Feb 24 09:48:20 EST 2008

I suspect, as others have suggested that, seawater is causing your problems. My tank has never seen seawater - at least in mine and the po's ownership time.  I only flush with freshwater - using the shower head, and never had an odour problem.  The only time I open the seawater intake seacock is about 4 times a year when I open and close it a few times to ensure it does not freeze up.

Try the fresh water approach first - using a fan will only move the odour and not eliminate it - may make the cockpit unusable when at anchor or mooring when the wind wafts the odour aft!

Indigo C&C35 Mk III 
Southport CT 
  ----- Original Message ----- 
  From: David Risch 
  To: cnc-list at cnc-list.com 
  Sent: Sunday, February 24, 2008 8:05 AM
  Subject: Re: {Stus-List} Mr. Wizard Question re: holding tank venting

  Sorry all two important pieces of info was ommitted.  The tank has two large vents (so blowing into tank will blow out other vent...and hoses were replaced...

  David F. Risch

  (401) 419 4650 cell

    From: Russ & Melody <russmel at telus.net>
    Reply-To: cnc-list at cnc-list.com
    To: cnc-list at cnc-list.com
    Subject: Re: {Stus-List} Mr. Wizard Question re: holding tank venting
    Date: Sat, 23 Feb 2008 22:23:50 -0800

    Hi David, 
            As Roger and Ed suggest, if the smell is in the head area while flushing (after a period of non-use) the smell is coming from rotting things in your intake hose. 

    In regards to the fan question, do not install it to push into the tank! Any slight leak in the tank fittings, especially inspection hatch (if fitted) will cause tank fumes to be blown constantly into the cabin (not just while flushing).
    Fan installation to pull from the tank is simply a waste of power unless you are going to install another vent. The fan won't pull anything from the tank if it can't be replaced. However, I don't think this is the proper solution for any holding tank problem.

    You really need to verify where the odour is coming from, a simple list.
    Intake hose: smell is strong while flushing. Outlet to tank: smell is strong outside the head space while flushing. Persistent smell in the boat: leaky or old hose/fittings, plugged vent. Strong smell outside the boat (especially while flushing: tank needs to be emptied more often. 

            Regards, Russ
            35 mk-1

    At 09:59 AM 2/23/2008, you wrote:

      Since most of you seem to be scientifically inclined than I, I thought I would pose the following question;

      Tired of hearing "what's that smell" upon flushing the head I am installing an in-line fan (micro-amps) to actively vent the tank.  The fan will be next to the tank...should I place the fan so the vent pushes air into the tank or pulls air out of tank.  Not much difference in my mind...but then again see the first sentence...

      David F. Risch

      (401) 419 4650 cell

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