vented loop between the toilet and holding tank

[DannyS]

Hey Peggie,
I'll be installing a new PHII, hoses and tank this spring and I was looking through the installation instructions for the PHII. For the below waterline installation, it shows a vented loop between the toilet and the holding tank. I don't recall a vented loop in that line when I ripped out the old system. Is that something I need if I don't have a macerator and overboard discharge? I'll only be running the discharge up to a deck pump out fitting.
Another thing, I am trying to fit a larger holding tank into the space where the old tank sat and I think I may be able to have the discharge line exit out the bottom of the tank but I'm not sure that's such a good idea. What do you recommend, out the side an inch or so off the bottom or out the bottom? My rationale for not going out the bottom is that it will always have "stuff" in the line, even after pumping out.

 

[Peggie Hall HeadMistress]

That illustration includes everything but a kitchen sink!

All those vented loops only really belong in any line that eventually ends up at below-waterline thru-hull. If you're only gonna be flushing into a tank that can only be emptied by pumpout, you don't need ANY vented loops except the one in the intake...pay careful attention to where it goes!

However, if it's uphill all the way to the tank from your toilet and/or more than 6', you might want to put a loop--not necessarily vented, just an arch--right after the toilet that the flush only has to get over...then gravity can do the rest. Less pumping, less flush water, less to run back down to the toilet.

 

[DannyS]

Thanks Peggie! That's kinda what I thought. Any thoughts on the pump out line coming out of the bottom of the tank?

 

[Peggie Hall HeadMistress]

You mean fitting ON the bottom, or...

...on a vertical wall AT the bottom?

The top of the tank is best place for all fittings (pickup tube inside the tank for the discharge)...but because that requires at least 5" of clearance above the tank, it's not always possible.

A discharge hole IN the bottom of the tank is a horrible idea unless a) the entire tank is above waterline...b)you plan to spend most of your time in open ocean more than 3 miles from the nearest point on the whole US coastline...and c) you want to be able to use gravity to drain the tank instead of a pump. And even then it's not a great idea. Since the Great Lakes are too far from the ocean for any of that to apply to you, don't even consider it. 'Cuz you'd have to install the pumpout line with a trap and a shutoff valve at the tank.

So that leaves AT the bottom the tank as the only place to put it...which is where the discharge is located on all "off the shelf" tanks in stock at marine stores.

 

[DannyS]

I won't have 5 inches above the tank so it looks like the fittings will go on the sides.
Thanks Peggie!

 

[Peggie Hall HeadMistress]

Hold it....we're not done yet!

I won't have 5 inches above the tank so it looks like the fittings will go on the sides.

The pumpout hose the comes from the tank at the bottom is almost always the first to permeate 'cuz it's always full of standing waste to the level in the tank. A piece of hard pipe (sched. 40 is just fine for this) is the solution...it needs to be only as long as the tank is high.

Search the previous threads in this forum for instructions to install it and connect it to hose.