Holding tank pick up tube/retrofit

[Skipper]

I figure this is a common need, but couldn't find the exact answer in search.
Recently installed new holding tank. All is good except pump out only empties 3/4. It's a low profile rectangular 5 gal tank. Capacity is usable for me, but sure would like that extra 25%.
I put an elbow fitting at the discharge during install, at the time not knowing about pickup tubes. I'd like to replace it with a pickup tube assembly that will screw into the existing threaded port. Is there such a thing?

 

[Peggie Hall HeadMistress]

I wish you'd checked in here before you bought a tank 'cuz Ronco Plastics Ronco Plastics Marine Catalog makes TOP quality water and waste tanks for a very reasonable price and has more than 400 shapes and sizes, over 100 of which are non-rectangular (which means you might be able to fit a larger one in the same space), and they install fittings in the sizes and locations specified by the customer when they make the tank.

If the discharge fitting is at the bottom of the tank ,you wouldn't be able to add a pickup tube to it. The only thing you could do is plug the existing discharge fitting and install a new fitting in the top of the tank with a pickup tube to the bottom...which would not be that hard to do, but it would make lot more sense just to replace the tank with a larger one. Actually, there is one other thing, not what I'd recommend, but possibly doable: put a shim under the other end of the tank to tip it so that everything in it runs to the discharge fitting.

However, I'm thinking that you'd actually be a lot better off with an "MSD" portapotty ("MSD" in the model number means it's designed to be permanently mounted and is fitted for pumpout...no need to carry off the boat). A 5 gallon model holds 50-60 flushes...you'd need at least a 30 gallon tank to hold that many from any marine toilet, manual or electric. No moving parts to maintain, no hoses etc using up a quarter of your storage space...and you could even plumb it to be pumped out or--by adding a y-valve and overboard discharge pump--dumped at sea. Less than $200 for the Thetford 550P MSD or the SeaLand Sanipottie 965MSD.

Something to think about anyway...

 

[Skipper]

Thank you, Peggy.
I can't plumb to the top of the tank, due to cabinetry.
Good to know pickup tube can't be done, saves me looking
I should have looked at MSD prior to the refit. But now I've got new Raritan head, new tank, and hoses. All at the expected time-gobbling labor, and costs.
I thought about the tilting idea. Can't do it permanently due to the vent being on the same side as the discharge. It would block up the vent when it reached that level. However, if desparate I can unfasten it and tilt it momentarily for a final pump out.
Thanks again.

 

[Peggie Hall HeadMistress]

In that case we might want to put our heads together to figure out where you can put larger tank that isn't a rectangle. Check the prices of 10-15 gallon tanks in the Ronco catalog, then send me a PM if you want some help...I can find good locations where you'd swear would never work that don't require taking a sawzall to the boat to get one in.

 

[Skipper]

Thank you again, Peggy.
I looked at all those tanks prior. There is room in there for a slightly larger tank, wedge-shaped on one side, but it would have to be custom, and properly measured first. Then it would have to be fit with custom supports, etcetera.
There is no other space for a tank, unless I want to give up drawers and modify the cabinetry, cut holes, route hoses, and so on. Sawsall City.
I'll ipload install pics of the new 5 gal if I can find them in a previous post.
Thanks again for your advise.

 

[Skipper]

Hi Peggy.
Just to show the restrictions and why had to go with 5g tank. (Pics)
The wood box assembly on the Vberth is the support for the top pull-out drawer. It goes on top of the tank. The hoses connect on the left (aft)there. So only tiny bit more room forward, and to port if had a custom wedge shaped tank. It's actually less room than it looks.
Would have been giant pain and added expense for little increase.
Thanks again.