Proper Holding Tank Positioning

[Pete7]

That's an excellent picture is the tank stainless steel?

Pete

[peghall]

I suggest that you return that tank and order one from Ronco Plastics (Ronco Plastics (no relation to Ron Popeil and his pocket VegOginzuknife) They make TOP quality (50% thicker than any "off the shelf" tanks) molded poly tanks for a very reasonable price and have more than 400 shapes/sizes to choose from, including more than 100 non-rectangular. And they install fittings in the sizes and locations specified by the customer when they make the tank, eliminating the need to relocate any of 'em. Btw...they're "just down the road" from you in Tustin, so you can prob'ly get it in a week.

Ideally all fittings should be on the top of the tank, with a pickup tube inside for the discharge...however, because that requires at least 5" clearance above the tank, it's not always possible. But you do want the vent to be on the top--1" is the minimum I recommend...and you want both the vent fitting and the inlet from the toilet to be toward the centerline of the boat, away from the hull...so that when the boat heels, waste in the tank can't spill into the vent line and head discharge line.

[RHoodJr]

We are still in the design and planning phase of installing holding tanks in our CSY 44 walk over and I had a few questions that hopefully someone will have some answers to..

I like the design of a gravity system with the tank above the healed water line thus eliminating a bunch of other plumbing features.

However, with a gravity tank installation how close to vertical and directly above the thru hull do you need to be for this design to work?

Could a ball valve be placed on the vent line so that when closed the pump on the toilet could be used to aid a gravity discharge design by pressurizing the tank a bit and help push any content out and flush out the tank?

Your thoughts are appreciated.

[pressuredrop]

Originally Posted by RHoodJr

However, with a gravity tank installation how close to vertical and directly above the thru hull do you need to be for this design to work?

Could a ball valve be placed on the vent line so that when closed the pump on the toilet could be used to aid a gravity discharge design by pressurizing the tank a bit and help push any content out and flush out the tank?

Your thoughts are appreciated.

dont know the answer to the first question but for pure gravity drain id think youd want at least 2" hose/seacock... given the standard 1.5" i elected to install a diaphram pump to pump the tank out, not trusting it to always drain completely on its own

my tank is epoxy/glass glass into the side of the hull... i glassed in thruhulls for all of the ins/outs with pvc ball valves on them so that the tank can me sealed to replaces hoses etc... never thought about using them to pressurize the tank, but i like that idea..... unless someone shoots it down...

[peghall]

Is that supposed to be a photo of the tank "on it's side?" If so, it's not...the inlet and vent are at the top where they belong, and the discharge is where it has to be unless it it's ON the top with pickup tube inside the tank that goes to the bottom.

However, as others have said...it's best to put all the fittings ON the top of the tank...but that requires at least 5" clearance above the tank. So I suggest that you return that tank and start over with one that's the right size/shape and has the fittings in the right locations to prevent most problems.

Ronco Plastics Ronco Plastics makes TOP quality tanks for a VERY reasonable price (maybe even less than you paid for this tank) and has more than 400 shapes/sizes, more than 100 of which are non-rectangular. And they install fittings in the sizes and locations specified by the customer when they make the tank.

With that many to choose from, you'll prob'ly find one that'll hold more and fit in a better location too. If you'd like some help with that, send me an email.

I have no connection with Ronco Plastics, btw...I was a Ronco distributor once upon a time, but sold my company over a decade ago, so I know their quality...which is outstanding.

[peghall]

Although all fittings on the top of the tank is preferable, it doesn't necessarily prevent tank contents from spilling out the vent or running back toward the head when the boat is heeled. That can be prevented even if fittings must be on a vertical surface.

Tank contents only spill into a hose that's next to the hull...when the boat heels, that hose runs downhill. So if the inlet and vent fitting are on an edge (top or end) that's AWAY from the hull--the edge that's closest to the centerline of the boat--tank contents run to the other side of the tank, away from the vent and inlet fittings, when the boat is heeled to one side...those hoses are running uphill when the boat is on the other tack. This works equally well whether the fittings are on the top or a vertical surface.

And while you definitely do NOT want a sag in a vent line where liquid can pool, it's not necessary for it to go up before running horizontally. In fact, the shorter and straighter it is, the better.

[peghall]

Sloshing will find that vent line.

Not if he puts a clamshell cover over the thru-hull.

[peghall]

It would have been lot easier to solve that problem by putting or cleaning/replacing the air valve that belongs in a vented loop.

[ccannan]

Dohenboy,

Are your referring to the Uniseal Slip fittings?

[peghall]

Looks good, but those hose connections--ALL hose connections in a sanitation system--should have TWO clamps, with screws 180 degrees apart.

[peghall]

Never seen the UniSeal called a "slip" fitting before... Here it is on the mfr's site:
UNISEAL Scroll through all the pages to see how it works and to get to their price list.

It's a great easy way to add or relocate fittings on the top of a tank, but not recommended for use below the level of any contents (so you wouldn't want to use it to put a new discharge fitting in the bottom of a tank)...and it's important to make sure that the hose doesn't put any stress pulling to one side, 'cuz that'll cause it to leak odor if nothing else.