ray lunder wrote:
Through the topside or the cabin side?

Through the topside...it should be as short, straight and as horizontal
as possible, and as Keith said, 1" or even 1.5", to provide the
necessary oxygen to keep the tank aerobic, which is key to eliminating
odor. The location on the hull depends on whether the boat is a
powerboat or sailboat. The vent thru-hull has to be high enough to keep
it above waterline when a sailboat is heeled...which can also mean that
the vent line has to be more vertical than is ideal.

However, water just splashing against the thru-hull won't put enough
into the tank to noticce, if any...in fact, if the boat is heeled to
that side, any that does get into the line will just run back out again.

Whether to run two vents to help accomplish that depends on the tank
location. It may not be practical to run a second vent line all the way
across the boat...and besides, if the second vent line is long and has
bends in it, it might as well not be there.

And btw...the tank should also be within about 6' of the toilet, because
that's as far as bowl contents will travel in the amount of time that
99% of people will spend pumping or leave their finger on a flush button.

This is a Par Mini tank with a 3/4" line.

An expensive tank that doesn't hold enough to be worth half its price or
the time and effort to install it...barely enough to last two people
overnight. If you haven't already installed it, I suggest you check out
Ronco Plastics http://www.ronco-plastics.com They make TOP quality
rotomolded tanks for a very reasonable price and have more than 400
shapes and sizes, over 100 non-rectangular, so you should be able to
find one to fit the same space that'll hold twice as much for less
money...and they install fittings in the sizes and locations specified
by the customer when they make the tank, which can make installation a
lot easier. We sold Ronco (no relation to the VegoMatic Ronco, btw)
tanks for more than 10 years (I sold my company in 1999)...I highly
recommend 'em!

--
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://shop.sailboatowners.com/boat_odors/