Dip tube or bottom fitting

M

mchad

Member
Member
Joined
Apr 30, 2001
RO Number
4410
Messages
250
I am replacing my aging aluminium holding tank with a 3/8" wall polyethlene tank from a custom mfgr. They start with a "holeless" tank and spinweld threaded ports to my spec. My current tank has three ports. The 1.5" input on the top, the 5/8" vent also on the top, and the pump out port on the bottom corner. When I speced out the new tank, i matched up the ports exactly, as to fit the current hose config. After sleeping on it, I realized I may be better with removing the pumpout port on the bottom of the tank and using a third port on the top, with a dip tube. This will give me the piece of mind of not having any holes below the "water" line of the tank, thereby giving it no chance to leak. Or am I fine with a nice wrap of teflon tape and a screw on PVC elbow with a 1.5" hose barb? My main concern was bending the existing hose to relocate it, but I could probably do it if its a better option. Then I also worry about the dip tube being pushed around during boat movement, and stressing the threads. Or is that not a concern?

Thoughts?
 
quote:
Originally posted by mchad

Click to expand...

I don't have any actual experience, but I suspect a dip tube would be better. Not so much because of possible leaks, but because with a bottom outlet (like on my boat), you end up with sewage in the hose connected to the outlet. The section with sewage lying in it will begin to permeate and will not last as long as hose that doesn't have sewage in it much of the time.
 
IMO poly doesent supply much friction to keep threads tight. I like your dip tube idea better as well.
 
Let me add, if you're having a custom tank made, a cleanout fitting on the top would be nice.
 
My tank has a dip tube, and I've have no problems with it.
 
What everyone else has said.

Having a dip tube, enabling you to pump the tank out from the top rather than the bottom is always best, for the reasons stated. But, be sure you have enough available space above the tank to accomodate the elbow fitting and hose connection. If your other fittings will also be on the top of the tank, you most likely do. You'll need between 4 and 5 inches of clearance above the top of the tank. In my nearly-40 years in this business, I've never heard of a dip tube failing due to stress on the external fittings. (I have heard, in the past, of metal dip tubes corroding away inside the tank - but everybody these days uses plastic dip tubes and fittings.) So I can't envision any problems at all.
 
Damn, I wish I had thought of that when I replaced my tank. Not as much for the concern of a leak lower in the tank, but to keep the waste from sitting in the hose!

And I second the idea of a cleanout port on the top of the tank.
 
When I first bought my boat in 2002, I had added a tank and it had a fitting on the bottom for the pumpout. After a few years, that fitting started to seep. While I was at a remote marina for Labor Day weekend. Not good. "Why does the boat smell like onions Dad?" I was able to get away and get to an auto parts store and buy one of those two part clay-like epoxy muffler repair kits and glom that around it and then clean everything up. It held for the rest of the season. But that winter I replaced the tank with a larger one in a different location, and went with the dip tube.

I just think you are asking a lot of that fitting - that is caustic material in there, you have temperature extremes, you have all kinds of boat motion and contents sloshing around with some force. The hose may move around a bit when vacuum is applied or removed or as heavy material moves through it. If you have the choice, why not make a nice "containment vessel" that can't leak and have your fittings be dry most of the time?
 
To me the most important thing is when it comes time to replace the macerator you won't have whatever is left in the tank draining out into the bilge.
Al
 
I do have a 8" cleanout as well. However, as it is, the tank is already in production and I can't change the specs. However I think I can use a 1.5" PVC plug in the lower port, and I saw a sealand dip tube kit that only needs a 3" hole for installation, which I can easily drill.
 
quote:
Originally posted by mchad

I do have a 8" cleanout as well. However, as it is, the tank is already in production and I can't change the specs. However I think I can use a 1.5" PVC plug in the lower port, and I saw a sealand dip tube kit that only needs a 3" hole for installation, which I can easily drill.

Click to expand...


Happy day. I spoke to the sales rep and he was able to change the order to eliminate the low port and install a dip tube. No chance of leaks now. Yay.

Now, how woudl one go about securing the tank? the AL tank had two flanges that were bolted into the deck of the bilge. The poly tank is just a box with no flanges...

I was thinking of some aluminium angle strips and a couple of straps maybe?
 
quote:
Originally posted by lobsta1

To me the most important thing is when it comes time to replace the macerator you won't have whatever is left in the tank draining out into the bilge.
Click to expand...
My macerator is above the level of the tank so no sewage sits in it. I did change the hoses and fertilized the bilge in the process.
 
You must log in or register to reply here.
Back
Top