However, speaking of combine vent:: I did end up with a problem of cross
over between my holding tank and my gray water tank. They share the same
vent and even though they are tee'd to gather about 3 ft above the tanks,
when ever the holding tank is full (I don't have gage) the liquid
flows over
into the gray water tank. Eventually I will discover the problem when the
gray water backs up into the ice box drain. YuK.

You're gonna have worse problems than that, Steve. There are animals
fats and other stuff in waste that are building up in your vent
line...they've prob'ly already reduced the diameter significantly and
will clog it. But you won't know it till both your gray water and waste
tanks have become pressurized...or you can't dump either one at sea
because of the vacuum created...or worse yet, a particularly strong
pumpout implodes a tank.

I'd also very surprised if whatever gasses are forced out your vent
aren't noxious enough to knock out any birds or insects within 50' of
your boat!

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://www.seaworthy.com/html/get_ri...oat_odors.html