Peggie Hall writes:

On a powerboat, no....'cuz powerboats don't heel. But on a sailboat,
if the inlet fitting on the tank is toward the hull instead of toward
the centerline of the boat, a loop--though not necessarily a vented
loop--is a good idea to prevent tank contents from running back toward
the toilet when you're heeled.

It's not necessary if the inlet and vent fittings are toward the
centerline because waste in the tank runs to the side away from the
fitting on one tack, the hoses run uphill on the other tack. Worth
remembering when you spec out an installation.

--
Peggie

Peggie,

thanks for all the great work you are doing! I read may of your
postings in different forums and benefitted a lot from your knowledge
in the installation of my holding tank.

However, this one I don't understand. When I read it first I thought
'shoot, my fittings are on the wrong side' since they are towards the
hull. But then I thought again and I don't see what's wrong about it.

Why is holding tank contents more likely to run out of the tank with
the fittings towards the hull than towards the centerline? Let's say
the fittings are on the hull side on the port side (as in my case).
Then, at a certain heel angle to port, the level of liquids inside the
tank will reach the fitting and overflow may occur (yuck). But if the
fittings were towards the centerline, why wouldn't the same occur when
the boat heels by exactly the same angle to starboard??

--Ernst
Columbia 32