Vented Loops?

[Glenn Newcomb]

Today I ripped out every piece of hose and the holding tank on my Hunter 33. I plan to replace all of the hose with SeaLand Odor-Safe and I have a new SeaLand holding tank on order as well. I am also replacing the 10 year old head with a Raritan PHII.I have read almost everything I can find about placing vented loops in the lines. I plan to install one in the 3/4" inflow between the head pump and the bowl as suggested in my reading. This should ensure that the pump will prime, while still providing safety against pump failure and siphoning.My question involves the 1 1/2" outflow from the bottom of the tank. I am installing a dual fitting at the bottom of the tank to allow for a run to the pump-out on deck as well as a run to a manual pump to a 1 1/2" thru hull. It is very rare that we would ever need to pump overboard and the 1 1/2" seacock stays closed all of the time. If I need to pump overboard, I would open the seacock, operate the pump (located 18" from the seacock)and re-close the seacock.Do I need a vented loop here? Because of the location of the 1 1/2" outflow fitting on the tank and the route the hose would have to take to get to a vented loop above the water-line, I am adding several 90 degree turns that would not be required to go directly to the pump and then the seacock. My feeling is that as long as the seacock stays closed, I am pretty safe.My old system had a Y-valve to pump from the head directly overboard or to the tank. It also had a vented loop on the 1 1/2" outflow side after the manual pump, but no vented loop on the 3/4" inflow. This was a very complex system with hoses and valves literally jammed under the settee. I want to avoid this complexity in my new system.Am I jeopardizing my boat by not having a vented loop on the 1 1/2" line?

 

[Ralph Johnstone]

Does not seem to be a problem ...................

.......... as this is exactly the arrangement on our H310. As long as the macerator pump discharge thru hull is closed after each pump out, I don't see how anything can go wrong.Regards,s/v Island Hunter

 

[Peggie Hall/Head Mistress]

Alternate Plan B

Spend about half as much money for the same quality tank directly from Ronco Plastics (they have more than 400 shapes and sizes to choose from), and--provided you have at least 5" clearance above the top of the tank--spec ALL your fittings in the top of it, with tubes to the bottom inside the tank on the discharge fittings (2). That not only eliminates standing sewage in the pumpout line, but eliminates the need for a y-valve or a vented loop in the tank overboard discharge line unless the top of the tank is below the waterline. Spec your vent fitting toward the centerline...that prevents a spill out of the vent when you're heeled...and do the same with the inlet fitting...even a half-full tank can overflow out the inlet and head back toward the toilet when the boat is heeled...putting the fitting toward the centerline prevents it and eliminates the need for a vented loop in the head discharge line.And if you haven't already done so, read the articles on replacing hoses and installing a head in holding tank in the HM forum reference library (on the forum home page). They include a few tricks that make the job a little easier.You're welcome to e-mail me if you want to discuss in more detail.

 

[Peter Boone]

Location of Vented Loop

I have a 1992 33.5 and I am confused as to where the vented loop in the 1 1/2" discharge line should be located. Should the 1 1/2 line from the head go directly to the holding tank or should it go to the vented loop and then to the holding tank? Discharge from the holding tank is via a deck pump out or to a manual waste pump and then to the thru hull without involving a vented loop. Any thoughts?

 

[Peggie Hall/Head Mistress]

Although not required...

I'd put either a vented loop or at least high arch at least a foot above the wateline at any angle of heel in the line between the head and the tank...'cuz when a boat's heeled over, even a half-full tank can head back down the hose toward the toilet. A loop--vented or not will keep it from getting there.I would definitely put a vented loop between the tank overboard discharge pump and the thru-hull. Same specs--at least a foot above the waterline at any angle of heel. If that's not practical, then make the one in the line between the head and tank a vented loop, not just a high arch. If you accidentally leave the seacock open, the tank will fill up, but the vented loop between the head and the tank will break any siphon before it get to the head to overflow it and sink your boat.