Dip Tube - Black water tank

[5teve]

Ok so you are gonna get a few randomw questions from me.

The black water tank was retro fitted by me into our boat about 5 years ago. I bought an off the shelf tank and the company did a pretty poor job of the dip tubes being about 75mm off the bottom of the tank.. leaving plenty of waste in there.

I made up some new ones using black poly fittings (common in Aus) however the dip tube keeps falling from the screw fitting as it has to be glued in - is Polyprop and even the best epoxy wont work.

Ive started looking for a PVC based fitting, essentially a reducing bush - but with the ability of having pipe glued in either side, or screwed in one side glued the other or with a through thread. External thread has to be 2" bsp (the tank has a number of these female thread bosses on the top) and the internal thread can be 1.5" or 1 1/4" or plain so I can glue straight through it.

I have been searching for a while - but cannot find anything... has anyone one found a fitting such as this that isnt custom made?

Steve

[Chotu]

When adhesive doesn't work, go mechanical.

without a picture I am not envisioning it properly I am sure.

but I am picturing a pick up on the top of the tank because you are talking about a tube and the length of a tube

what you should do is get some sort of reducing collar that will fit the tank and whatever size pipe you want going down into the tank.

either a very tight fit without threads or something threaded. Threaded would be even better.

if you don’t have threads, put a screw through it to hold it in place. Maybe two screws if you need to. That should be inside the tank.

But it looks like the environment in the tank, plus the fact that it’s all plastic stuff, means that adhesive don’t work incredibly well in this department. Mechanical fasteners are the way in my opinion

[hlev00]

You might check out Uniseal fittings. I believe Peggy Hall recommends them but search the forum for more detail. Here is one example https://www.cruisersforum.com/forums...ml#post1876390

[5teve]

Originally Posted by hlev00

You might check out Uniseal fittings. I believe Peggy Hall recommends them but search the forum for more detail. Here is one example https://www.cruisersforum.com/forums...ml#post1876390

That is a nice Idea... I wonder how 'removeable' they are? I could make a PVC assembly - slide it in.. and it sits there. When I need to do Maintenance I can slide it out..

The other huge advantage is I dont have to thread the assembly in what is already a limited space..

I wonder how the smell permeates through? I assume I would need to fix the pipework to stop it moving too?

Excellent idea.. thank you

Steve

EDIT - Even better they make compact PVC Bulkhead fittings too which would likely work!

[5teve]

Thanks Chotu

Appreciate your response. You are envisioning it correctly.

The tank has a 2" threaded hole in it. The dip tube 'assembly' screws into the hole.

The issue that i have is (apart from restricted height above the tank - another issue!) that any reducers I have have the 2" thread externally - and 1.5" or 1.25" internally - are tapered, poly and only threaded part way through.

This means that I cannot screw in a dip tube from the tank side and glueing has failed. A screw is an excellent idea except the amount of tube I can get into the reducing bush is minimal.. hence me using some ultra good JB weld..

So this is why I went onto PVC, hoping that I could find a through threaded (internally) reducing bush or a 2" external with a smooth internal I could just slide a pipe into and glue into place (or glue from either side) Being PVC we know its good for sewage and the solvent weld is just that.. it welds it.

Its this reducing bush that has me beaten.. i cannot find anything especially locally (aus)

Picture hopefully shows what i'm talking about - a bit!

Steve

[rslifkin]

The dip tube in my tank is glued together PVC and has held up just fine. Even if the joint from the main tube into the collar at the top failed, the tube would hit the bottom of the tank before sliding down far enough to disengage from the collar.

[5teve]

Originally Posted by rslifkin

The dip tube in my tank is glued together PVC and has held up just fine. Even if the joint from the main tube into the collar at the top failed, the tube would hit the bottom of the tank before sliding down far enough to disengage from the collar.

This is what I am aiming for I just cannot find the fittings.. as crazy as it sounds.. as I need a screw in 2" thread... and the pipe attached to that.. I can get close but without machining.. I cannot get all the way there.

Steve

[peghall]

This ain't rocket science!

Is there a female threaded fitting in the top of the tank? If so, you only need to "glue" using PVC cement or the "glue" of your choice a PVC pipe long enough to touch the bottom of the tank into a male thread-barb hose fitting. The outer diameter of the pipe needs to be the same size as the INNER diameter of the hose fitting. Cut the bottom of the pipe at about a 25 degree angle...any flatter and you risk solid waste and/or TP getting trapped under it, any sharper leaves too much in the tank.



If there is no female fitting in the top of the tank, use a Uniseal UNISEAL to create the opening...and again, cut the pipe long enough to leave enough to glue it into a thread/barb hose fitting.


Uniseals are not removeable...but there should never be a need to remove it,any more than you'd need to remove any other hose fitting for "maintenance." To rinse out the tank, just put put enough water into the tank VIA THE DECK PUMPOUT FITTING to cover the bottom to a depth of 4-6"...'cuz that sends the water into the tank at the bottom to stir up any sludge to hold it into suspension so it can be pumped out. Pump that out or use the tank discharge pump if you have one...repeat, repeat till you're pumping out clean water.

You're welcome to contact me directly if you need more help to do this.

--Peggie

[Bowdrie]

Some searching thru their site will reveal at least a million different fittings and parts, enabling the assemblage of most anything related to toilet plumbing.
https://marinesan.com/

[5teve]

Originally Posted by peghall

This ain't rocket science!

Unfortunately - in answer to your later question... Im in Australia and its seems harder than rocket science.. and possibly the root cause of this hardness is that I bought an off the shelf tank.. and trying to use domestic fittings

Originally Posted by peghall

Is there a female threaded fitting in the top of the tank? If so, you only need to "glue" using PVC cement or the "glue" of your choice a PVC pipe long enough to touch the bottom of the tank into a male thread-barb hose fitting. The outer diameter of the pipe needs to be the same size as the INNER diameter of the hose fitting. Cut the bottom of the pipe at about a 25 degree angle...any flatter and you risk solid waste and/or TP getting trapped under it, any sharper leaves too much in the tank.

Yes this is correct Female threaded hole in the top of the tank and what you describe is exactly what I am trying to do (having read many of your posts as a benchmark) The issue I have is that I cannot find a fitting that can go into the tank thread and has a through thread, or a any kind of double sided fixings (ei glue thread etc) that will go into the tank - The original was a poly reducing bush with a poly dip tube glued in but was far too short, I remade it the same way and it worked until the dip tube came unstuck (should have fricton welded it) so now i'm trying to replicate with PVC as that will work (I'm also looking at hard piping sections too)

It does look like uniseal have a bulkhead fitting in ABS I could use.. as long as I can confirm if the threads are compatible.

Originally Posted by peghall

If there is no female fitting in the top of the tank, use a Uniseal UNISEAL to create the opening...and again, cut the pipe long enough to leave enough to glue it into a thread/barb hose fitting.

Uniseals are not removeable...but there should never be a need to remove it,any more than you'd need to remove any other hose fitting for "maintenance." To rinse out the tank, just put put enough water into the tank VIA THE DECK PUMPOUT FITTING to cover the bottom to a depth of 4-6"...'cuz that sends the water into the tank at the bottom to stir up any sludge to hold it into suspension so it can be pumped out. Pump that out or use the tank discharge pump if you have one...repeat, repeat till you're pumping out clean water.

You're welcome to contact me directly if you need more help to do this.

--Peggie

Thanks for the info on the uniseal. I may not need them but they are a neat idea! As i have no disconnects in the system when I need to change the triscpid valves in the gulper pump - i have to remove the pipes - no easy feat.. so i'm looking at hard piping sections with threaded couplings as disconnects. Thats the reason I was asking.

Regarding flushing the tank there is a nice 6" screw in round hatch that I can open and hose out. However I do use noflex and its made a hell of a difference with no scale any more - just sludge. The Deck wash gets used when I actually find a pump out station (maybe one opertaional in Perth?) and I back flush it and empty it.

Appreciate yours and everyones input. I may well order some uniseals bulkhead fittings and see if they work.

Steve

[peghall]

You might want to actually TALK to the folks at Uniseal (which btw, is a part of an Australian company (Australian Global Services) You may even be able to find Uniseals in Oz. I'll give 'em a call to find out.



And to repeat my offer, you're welcome to contact me directly if you need more help.


--Peggie

[gonesail]

off topic but .. the new west epoxy .. gflex .. is advertised to stick to plastic. it is pretty tenacious stuff.

[peghall]

There are many types of plastic. So far no one has ever come up with a sealant that will bond PERMANENTLY to polyethylene. Heat welding is the only thing that works...and that's not as simple as most people think.


What part of world are you in, Steve?


--Peggie

[nofacey]

Uniseals are the answer
https://ronco-plastics.com/product/uniseals/

Used them in my holding tank, easy to install, zero leakage - and I believe I could have removed them if needed, by simply pulling out the dip tube, then removing seal. Not sure seal would be useable after....

[peghall]

No need to buy Uniseals through Ronco Plastics...the Uniseal Warehouse in FL sells direct. UNISEAL They're very nice people who will answer all your questions if you call to order instead of buying online. Uniseals are so inexpensive that they can be air mailed in a padded envelope.


Be sure to read and FOLLOW all instructions.




--Peggie