Best way to install a "dip tube" in existing tank?

[Chris & Lenore]

Our current holding tank has the pumpout fitting on the side, near the bottom of the tank. There is no "dip tube" inside the tank so the bottom quarter of the tank never empties.
I'd like to install a bottom pickup tube similar to our previous boat which allowed almost the entire tank to be pumped out.

There are the Uniseal's but are they strong enough to stay leak free with waste hose connected to them? Waste hose is so inflexible I wonder if it would exert too much force on the fitting/grommet? If it did, it might be impossible to keep the tube in position and close to the bottom of the "low corner" of the tank.

The other idea I had is to fabricate a tube that fits into the existing pumpout fitting from inside the tank. I can get to it via the cleanout and fit a smaller diameter tube through the tank opening and into the hose fitting that screws into it. 5200 should keep it in place - but the dip tube inner diameter would be smaller than the fitting and hose. An advantage is that I could shape this tube to reach the low corner of the tank and angle the end so it hovers close to the bottom.

Any suggestions? I hate losing so much tank capacity simply because I can't pump it all out.

Thanks,

Chris

 

[JamesG161]

Do you have a simple sketch of the tank? Just a rectangle?
Jim...

 

[Chris & Lenore]

It's just your basic rectangular tank. Like in the pic but with a 6 inch diameter cleanout in the top.

 

[Peggie Hall HeadMistress]

Yes, the Uniseal will remain leak free as long as there's no stress pulling the hose or pipe to one side. However, because there's always a possibility that something can be done to the boat later that would cause it to leak, the Uniseal is not recommended for use at the bottom of a waste tank

Is there a hatch above the tank that would provide the clearance you'd need to insert a pickup tube into the tank from the top? If not, how hard would it be to pull the tank out and install a pickup tube in the top of the tank? And finally...you'll need a about 4-5" of clearance above the tank for the hose connection when the tank is back in place. Have you got that much?

If we can put it in the top of the tank, this would also be a great time to put a new 1" vent fitting in the tank.

 

[Chris & Lenore]

Can't have any fittings on top of tank - only the sides.
That's why I was thinking of a tube that would insert from inside the tank into the lower screw in hose fitting.
Those are 1 1/2 ID, so if I used 1 1/2 OD it should fit. Then shape the tube (with heat) to keep an angle cut end close to the tank bottom.
Unfortunately, this reduces the effective ID by a quarter of an inch. Also a smelly and messy job...

BTW - I have increased the vent hose to 1 inch ID. My tank had a three inch diameter plastic "puck" welded/melted to the tank that was drilled and tapped for 1/2 inch. It was large enough to redrill and re-tap for larger fittings.

Chris

 

[JamesG161]

There is no reason to insert a dip tube inside a bottom fitting to draw off a tank that has a top air vent.
If you can install a Wye type Tee fitting
http://www.homedepot.com/p/1-1-2-in-PVC-DWV-All-Hub-Sanitary-Tee-C4811HD112/100344315
you might be able to share an existing bottom tank fitting.

This is just "food for thought".
Jim...

 

[Peggie Hall HeadMistress]

There is no reason to insert a dip tube inside a bottom fitting to draw off a tank that has a top air vent.

I'm not sure what you're suggesting, Jim...but I do know that you do NOT want a discharge and vent to share any plumbing.

And btw...a fitting is either a tee (T) or a wye (Y). It can't be both.

Chris, I have a couple of ideas...if you'd like to bat this around on the phone send me a PM.

 

[woodster]

I do know that you do NOT want a discharge and vent to share any plumbing.

that would create an anti syphon and the contents would not come out

 

[JamesG161]

I'm not sure what you're suggesting, Jim...but I do know that you do NOT want a discharge and vent to share any plumbing.

Think outside the box!! (pun intended)

A Wye is a speciality Tee, kinda like a square is a rectangle.
________
My Hold tank's RV outlet shares (using Street Lateral, or 120° angled Tee, sometime called Wye from it "Y"shape)
with my Macerator and is Outside the tank.
______
Who knows it might even work for him.
Jim...

 

[alexco38]

That's the common problem for CS yachts. The bottom of the tank is 4 inches from the pumpout fitting.
HMP sells an curved insert that reach the bottom at $$$.
I found that a 1-1/4 bathroom drain trap fits inside the screw in 1-1/2 hose barb. The drain trap is thin wall thus it doesn't reduce the diameter by much. There is no need for thick wall inside the tank.
I use heat gun to bend the plastic drain trap into a curve.
Been using it for 9 years.