Holding Tank Vent

[Stu Jackson]

A good, long and detailed discussion of these issues is here:  http://c34.org/bbs/index.php/topic,5755.0.html

[dbpaul]

PaulJ,  Thanks for the picture.  What is the larger cylinder in the stern area?  It looks like a blower. 

Blower vents engine compartment.................

[Roc]

Here's the vent line I added.  I kept the one going to the stanchion because it kind of adds 'cross ventilation' in a sense.  Also shown is the thru hull I placed toward the bow, just below the rub rail. I led the new vent line forward into the v-berth port side cabinet.  That's where it exits.

[Jim Hardesty]

Roc,
I feel Catalina shorted me.  My 2001 doesn't have an inspection/cleaning port.  Or did you add that?
Jim

[Exodus]

Roc,

Is that a one inch hose and fitting that you added?

I have ordered a one inch thru hull, but others have said one inch is too large for the space between the tank and settee cushion.

[Peggie Hall]

Roc...I'm guessing that you used hot water hose for your new vent line because water hose is a LOT cheaper than sanitation hose...that's why builders like to use it for vent lines. Unfortunately, it also permeates very quickly.  So when you start to notice odor inside the boat, it's almost certain to be the tank vent line. Use Shields or Trident #148 when you replace it.  If you also used water hose for your toilet intake line, replace it with #148 sanitation hoses too...fresh water hose is not rated for below-waterline use.

I'm also guessing that you had to splice it because you mis-measured?  

Btw...you don't gain anything by keeping the line going into the stanchion...the slit is so small and is also on the aft side of the stanchion that no air can possibly get it. Besides, it's prob'ly already clogged with dust, pollen and maybe even a dirt dauber nest by now.

[Roc]

Peggie, actually when I did this, I consulted you and you said how to route it (slow upward slope vs. straight up to rub rail).  I used sanitation hose.  The original vent line water hose from the factory has since been replaced with sanitation hose (old picture).  Also, when I consulted you, you suggested to keep the original vent line and it's not clogged.  No splices, everything is one piece.

I believe it's 1" hose, it's whatever Peggie suggested when I did this.

I guess Catalina doesn't add the inspection port anymore. Mine came like that from the factory and that's where I added the new vent line.  My thought was if anything gets screwed up, all I have to do is buy a new inspection port cover, and no issues with the tank itself.

[Peggie Hall]

Roc...  Ahhhh...old photo!  Whew!  Otoh, it does provide an excuse to remind anyone else doing this project not to use water hose.

I suspect I advised keeping the original vent line because although it isn't accomplishing anything it can't hurt to keep it...and it's easier to just leave it than to remove it and have to mess with putting a threaded plug wrapped in Teflon tape in the tank fitting.

Lance... a tank vent--ALL tank vents--actually have two primary purposes--to provide an escape for air in the tank displaced by incoming contents (water, fuel, waste)...and to provide a source of air to replace contents as they're pulled out of the tank by the pump (water, fuel, macerator, pumpout).   

When it comes to waste tanks, the vent serves a third purpose: to allow the exchange of fresh air from outside the tank with gasses inside the tank that's necessary to maintain an aerobic environment in the tank.  The only reason for an aerobic environment  is the elimination of odor, 'cuz organic material breaks down equally well in both aerobic and anaerobic conditions...but when it breaks down anaerobically, it rots and becomes septic...generating gasses that are toxic, even lethal in enough concentration--sulfur dioxide and hydrogen sulfide which are foul smelling, and methane, which is odorless but toxic and also flammable. It's these anaerobic gasses which require all WASTE tanks to be vented to the outside of the boat.  However, when organic matter breaks down AEROBICALLY it converts to CO2, which is odorless and harmless.  That's why compost piles require regular "tossing"--to aerate them...and why sewage treatment ponds all have geyser fountains in 'em--to aerate 'em (for which everyone downwind is grateful!).  It also explains why decorative water elements in malls and office buildings always have waterfalls and fountains...to aerate the water. Without 'em, the water would become a stagnant stinky primordial soup. 

So the tank vent is a very necessary part of the system. When a waste tank vent can't supply enough air exchange to create an aerobic environment, some mechanical help may be needed...but that's rare in tanks smaller than about 50 gallons.

[Roc]

Peggie,
The large vent I added does just what you claim, it allows air in to keep things in an aerobic environment.  I started out using KO, but now use Odorloss and there is absolutely NO boat head smell.....  I had this set up since I bought the boat new and the inside always smells fresh.  I appreciate your expertise and thank you for the knowledge you've shared with everyone.

[Lance Jones]

That's what I love about this forum! You learn something new all the time. Thanks Peggie!

[Exodus]

Roc,

One more question please:

What kind of drill bit did you use for the thru hull and how thick was the glass in that location.  I assume it would be better to drill from the outside so that any rough edges would be on the inside.

Thanks!

[Peggie Hall]

Lance, I just noticed you're in Lake Lanier...I was there for 25 years.  At Holiday for the first 10, then at UYC. Left in '01 to look after my dad here in AR.

[Ted Pounds]

Often the best technique is to drill from both sides.  That is: start the hole from one side and drill until the tip of the bit just pokes through.  Then use that hole to line up the bit and complete the hole from the other side.  That leaves you with no rough edges on either side.  Another technique for large holes like this is to drill a small pilot hole first then drill from each side (one at a time), meeting in the middle.

[Mike and Joanne Stimmler]

One other trick is when you are using a hole saw type drill bit, after you drill the pilot hole, and you are drilling from the outside where you want a nice smooth edge, first start drilling with the drill in reverse, then when you get through the outside layer of the gel coat, you can switch to forward to finish the hole.   

Mike

[Roc]

I used a hole saw bit with the correct diameter for the thru hull.  Drilled from both sides as others have said. Start drilling in from the outside, until the center bit pokes through.  Then drill out from the inside of the hull.