engsol wrote:
On Mon, 10 May 2004 15:21:17 GMT, Peggie Hall wrote:

good comments snipped

It does require two vents, and the fan should be be an
exhaust fan that pulls air through, not one that pushes air into the tank.


Peggie, I wondered about your statement above...until it occured to me
that you're entirely correct. The reason (tell me if I'm wrong) is that by
sucking air out, a slightly negative tank pressure is created. This prevents
odors from escaping into the boat via the vent loop, (or any other "air leak"),
which it would if the tank had positive pressure.

I dunno about that...I think you're over-thinking it. Compare it to an
attic or "whole house" fan in a house, or even a hood fan over a stove.
They pull air out of the house because that's the most efficient way to
do it. To replace/exchange air being pulled out requires a source...in a
house, the source is open windows or doors...in a holding tank tank it's
a second vent line.

I'll probably try this when I (finally) get my own boat, but I'll be sure to
make the fan easily replacable, since I suspect the "fumes" will be
somewhat corrosive.

More often than not, a single 1" diameter short (3') straight vent line
will work all by itself. It's only when the tank location makes a
short straight vent line impossible that more complex solutions are needed.

--
Peggie
----------
Peggie Hall
Specializing in marine sanitation since 1987
Author "Get Rid of Boat Odors - A Guide To Marine Sanitation Systems and
Other Sources of Aggravation and Odor"
http://69.20.93.241/store/customer/p...40&cat=&page=1