Holding Tank Fittings Help w/ discharge

[DustinM]

Hello.
I looked far and wide for another thread of someone with this question but cannot find a solution. I have just received my new Ronco Plastics holding tank yesterday, and it came with the spinwelded, female, threaded holes in the top of my tank that I requested. I have qty 5. A vent, 2 intakes, 2 discharges (pumpout and overboard).

Now that I have it, I am struggling immensely with the hardware necessary to set up the discharge fittings. The vent and intakes are very simple. Male NPT threaded to hose barb fittings. But for the discharge holes, how do I accomplish the installation of a pickup tube and a hose barb onto the same hole? What fitting accomplishes that? If you can, please be as specific as possible. I stood in the PVC section of Lowe's this AM with my new tank in the cart next to me for about 2 hours trying to come up with a solution.

It is a flat bottomed tank, so a simple PVC pickup tube with a 25 degree angle cut at the bottom is how I'd imagine to implement the portion within the tank. But what does that vertical pipe connect to at the top of the tank that can also connect to a hose barb once outside of the tank? I looked at many bushings but could not figure out how to get any to work for this use. I went to a plumbing supply store, too, and they did not know how to help.

I have called Ronco a few times and spoken to different people but I don't believe I'm explaining myself well enough via the phone, as it's not been helpful. Hoping the attached picture of the top of the tank can help, as well as my diagrams. Please note, implementation 1 and 2 are both just options, not that I'm considering one for one discharge hole and one for the other.

Thank you very much in advance. I really feel like someone has surely gone through this already with how often Ronco is suggested.
I've heard if you say Peggy's name 3 times you might even be lucky enough to have her show up in your replies :lol:

 

[HeadMistress]

But what does that vertical pipe connect to at the top of the tank that can also connect to a hose barb once outside of the tank? For the discharge holes, how do I accomplish the installation of a pickup tube and a hose barb onto the same hole?

First you'll insert the pickup tube into the tank....Then you'll cement the top end of the pickup tube INTO the threaded end of the of a thread-barb male hose fitting, which can be either a straight fitting or a 90.

If you don't already have the pickup tube, you'll have to buy a piece of PVC pipe that has an OD (outer diameter) that's the same size as the fitting ID (inner diameter). It should be long enough to reach the bottom of the tank--cut at about a 25 degree angle with just enough left at the top to slip into the hose fitting.

If you need more help, send me a PM, either here or in cruisersforum.com where I'd already posted the same reply.



--Peggie

 

[DennisB1]

I would talk to a business like Marine Sanitation in Seattle. They have some of the fittings you need. Also I have made on a metal lathe adapters to connect the dip tube to the 1 1/2 pvc fitting. You can buy on line pvc solid round bar stock to make the fittings which glue together. I would not use the 25 degree bevel cut but rather a 90 degree cut to get closer to the tank bottom. Radius the inlet pvc wall to improve flow into the pickup tube. Hopefully you have a toilet that macerates all the incoming sluge. I use a 1.0 inch Hose for the overboard discharge (which I don’t use often) and 1 1/2 for the deck discharge.

 

[Taras]

Curious why the discharge fittings are not at the bottom side of the tank? Perhaps there was not space? Seems like sucking the contents of the tank from the bottom side of the tank would be easier? I'm asking because this is a project I may have to undertake.

 

[DennisB1]

Taras. If you have to remove the dip tube for some reason with waste in the tank you will s appreciate having the tube coming out the top.

 

[HeadMistress]

A discharge fitting at the bottom of a tank will have standing waste in the discharge line to the level of the tank contents. Inlet and discharge fittings on the side or end of a tank reduces tank capacity because waste will spill into the inlet line when the level in the tank reaches the bottom of the inlet fitting...pumpout can only remove contents till the level reaches the top of the discharge fitting.

Putting all fittings including input and discharge fittings on the top of a tank with a "diptube" inside the tank eliminates not only solves both those problems but eliminates standing sewage in any line.

Unfortunately it's not always possible, though...'cuz 1.5" fittings in the top of the tank need at least 5" clearance above the tank, which many installations don't provide. So height is definitely a factor to consider when replacing a tank.


--Peggie

 

[ranger58sb]

Dustin, Ronco will make up the dip tubes/upper fittings for you if you want.

-Chris

 

[ranger58sb]

Curious why the discharge fittings are not at the bottom side of the tank? Perhaps there was not space? Seems like sucking the contents of the tank from the bottom side of the tank would be easier? I'm asking because this is a project I may have to undertake.

We found it WAY better to have top-mounted dip tubes.

In our case, partly because we were focused on increasing tank capacity, and dip tube -- along with top-mount inlet fittings -- got us from a nominal 40 gallon tank (about 28 gallons actual) to almost a real full 40 gallons capacity.

And then it's easier to deal with overboard pump-out systems when the outlet hose is already clean. (We used two outlets, one to the deck fitting for pump-out, the other to a macerator pump for overboard discharge... which we can seldom do due to our location.)

-Chris

 

[Bacchus]

On our last boat the low 40 gal tank lost 20-25% as a result of the end/side discharge. Pumping out would suck air at roughly 2" depth and tank was only 8-10" hi ( don't recall exactly). The tank sat at the edge of a raised platform and I was able to remove the hose barb, insert a pvc trap fitting with the hose barb/ hose attached to the other end of the trap.
Result was a significant increase in usable tank capacity. For end of season cleaning I could stand on that side gunnel and get close to emptying the tank as the trap prevented sucking air until all the liquid was gone.

 

[Barking Sands]

A discharge fitting at the bottom of a tank will have standing waste in the discharge line to the level of the tank contents. Inlet and discharge fittings on the side or end of a tank reduces tank capacity because waste will spill into the inlet line when the level in the tank reaches the bottom of the inlet fitting...pump out can only remove contents till the level reaches the top of the discharge fitting.



--Peggie

You can solve both of these side mounted hole issues with a few extra pieces of PVC. On mine, both the discharge and inlet are on the side. For the inlet at the top, side of the tank I have a 90 degree fitting coming out of the tank that angles up and then going to another 90 degree fitting. They are both oriented to have the water flow slightly above the tank and then down into the tank. Using the right combination of either two or three 90 degree fittings (or a U) the travel of the inflow can be raised above the tank anywhere from a 1/2 inch to as much as you want, sort of like a vented loop might be used (but without the vent). The PVC fittings are cheap and once you have them, any desired configuration can be achieved. Mine is about equal to the top of the tank so I lose a small amount. Its not quite angled like the first pic but close. If it was a problem I could just rotate the fittings 20 more degrees and get some additional room or convert to a full U, but it has not been an issue.

For the discharge line on the bottom side of the tank I just added a PVC ball valve coming right off the tank. There is actually a Y coming out of the bottom side fitting with one side going to sea cock overboard and the other going to vacuum pump out. The ball valve prevents contents from sitting on top of the sea cock in that hose for extended periods. The only time the ball valve is opened is when the sea cock is going to be open as well for overboard draining.. Then close the ball valve and then sea cock and the overboard discharge hose always remains empty. Only a small additional amount of contents stays in the PVC fittings just prior to the hoses.

For pump out I have found that as long as the hose/fitting extends down as it exits the tank that the entire contents do get emptied during pump out regardless of sucking air. It just takes a few minutes extra. I also have the entire tank angled slightly to that side. As a result there is maybe a 1/4 inch bit of water that remains. Of course that depends on how the manufacturer made the exit holes from the bottom wall. If they are an inch above there isn't much you will be able to do about that inch of contents. The Ronco tank sent to me is nearly flush. And then angling the tank slightly so the contents pool at the fitting end helps too.

Besides, a dip tube will not get out the entire contents either. And generally we flush fresh water through when at the bottom. Also a dip tube is much more prone to blockage.

I would estimate I can use 90-95% of this tank with the side discharge. Thank god because I am really space limited and its only about a 12 gallon tank.

I am not opposed to either. But side discharge can be configured so that it does everything top mounted can do and in some cases better.