Designing a holding tank..sources of information, please?

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NealB

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I didn't want to hijack the other current holding tank thread.

Tektanks have quoted me £725 for a custom made poly tank, with a 4 week lead time.

Now, I hear that they're a very good company to deal with, that they are very knowledgeable and helpful, supplying excellent products and service.

However, that seems like a lot of money to me, particularly as a friend has offered to make one for me in grp.

Can anyone point me in the right direction for information such as: size and shape of baffles? is there a critical clearance between the bottom of the pump-out pipe and the bottom of the tank? Is there a minimum bore for the breather pipe?

Any advice most gratefully received.

Or am I just a mean-minded, penny-pinching, cheapskate?

Thanks.
 
Yes! Get it done properly!

Raid the Tek Tanks site and you will get information sheets on tank design.

Normally you would not need baffles unless the tank is long and thin. If I rmember rightly my pump out pipe is about 35mm from the bottom, although I have not connected it yet, just a blanking plug on the fitting. Breather should be minimum of 18mm, but 25mm is usual.

If you want to save dosh, have you looked at whether you can use a standard tank from Vetus pages 90/1 of their catalogue. They are much cheaper than a custom tank, but you are stuck with the standard sizes. Alternatively cleghorn Waring / Jabsco have a range of tank systems and a few tanks as do Lee Sanitation

Hope this helps
 
You probably are a cheapskate, but there's lots of info about to help you decide whether it's worth the risk! Take a look at the Lee Sanitation website, especially their data sheet on holding tank systems, and their installation guide. Note that they recommend that the pump-out pipe should be cut to a 45degree angle at the bottom end, and should reach to within a few mm of the tank bottom.
 
I had excellent service from Tek Tanks too.......but what I found most useful...and yes it is a fag ...but when you are spending that kind of money you need the thing to be right....was to make an exact size mock up out of 1x1" softwood and hardboard and play with it in the boat until its right ,making sure that the inlets and outlets are in the right place....and that you can get it down the companionway...and you have a method of securing it.....and then present it to Tek and tell them to make it.
 
We designed our system around a standard size "off the shelf" tank after a similarly expensive quote for a tank. Whole cost including tank, pump, diverter valve, tank fittings, new pipework, deck outlets, loads of SS jubilee clips etc etc was under £500.
 
I guess we need to know the full spec. of your proposed tank to be able to decide if the Tek Tanks quote is good value. I have to say that a holding tank is an item in which I want to have complete confidence. Failure of a DIY unit hardly bears contemplation. We had our tank made by Tek Tanks from a mock up we made in ply because the installation was quite complex and the shape was quite irregular. THere was no way a standard tank would fit. I drew up some scale drawings from the mock up ( you can send them the mock up) and they were incredibly helpful and supportive and patient with my amateur efforts.
The result was a tank that fitted perfectly and worked perfectly ( they ran an eye over my proposed plumbing and pronounced it good). THe bottom line is that what might seem to be a lot of money is an excellent long term investment in a reliable system.
If you do have space for a standard tank certainly look up Vetus, Leesan and of course Tek Tanks.
BTW, I would NEVER consider a flexible holding tank.They tend to wobble about and chafe with unpleasant consequences.
 
It's just a simple shoebox shape: 1300 x 840 x 280. All nice right angles and flat planes.

Unfortunately, I've not found a standard tank which makes effective use of the available volume.

However, having had the lovely job of cleaning up after the old galvanised tank split at a seam, I have no hesitation in agreeing with all those who preach the need for a reliable system, even if it seems expensive (hey - it's a boat!).

Thanks again for all the replies, as a result of which I've got a few more requests in for quotes. Watch this space.
 
I made my holding tank from 12mm ext. ply with a removable top. The inside has a couple of layers of fibreglass and finished with a waterproof resin, the top then fitted and sealed. Have just finished the fourth year of use with no problems or smells and cost less than £100. By been tight doesn't always mean you end up in the [--word removed--].
 
Yes, your constraint is height. This is very low compared with standard tanks - and you still have to add the fittings. Presumably this is a pumped system, in which case you might consider having a stepped design like the Vetus ones with the pumps and fittings on one end of the top (see p90 of catalogue). You will definitely need baffles. The Tek Tank calculator suggests 4 in that length. It also gives a volume according to the calculator of over 170 litres which is very large. With a typical 6-8 litres per person per day this gives around 12 days capacity for a crew of two! If I have my sums right.
 
The 280mm height allows for elbow fittings on top.

It's a pumped system in the sense that, at present, the only way of emptying it is via a marina pumpout (the loo itself can be directed to either tank or sea). I may take the opportunity to arrange an alternative tank emptying system.

The burst tank is one of two onboard - the other is the bigger: that will be replaced, in turn, in the not distant future.
 
You are into much bigger money if you use a pump system. Couple of hundred for the pump or macerator plus another outlet unless you can arrange to use the existing direct to sea outlet. See why you need such big tanks if you can only use a marina pumpout. It is more common to have both so that you can discharge to sea once you are clear of coast.

Don't know if you have the space, but there is a trend toward gravity systems using bulkhead mounted tanks on the KISS principle. Examples in the Vetus catalogue and Tek Tanks made a similar custom design for me to fit my bulkhead space.
 
also check out the new Vetus tanks in their catalogue. Not the off the shelf plastic ones but the new collabsible ones which are inflated in place, and cured with a UV light to become rigid. They have a quality liner inside and look quite good, The great thing about them is the ability to be folded/rolled up to fit into a space and when inflated take up the shape required. We currently have a 160 ltr Vetus inflateable which I dont like but this one looks much better and if they will introduce it into the US catalogue,I will certainly think about fitting one. Also the ultrasonic tank sounders.
 
Yes, I am considering one of these, but they are expensive . A 100 litre tank is about £750 with installation kit and fittings - nearly 3 times the normal flexible tank and on a par with a similar size custom tank. But of course can be used where access is difficult.
 
Re pumping out. Consider A Lavac loo and diverter valve arrangement. Using our Lavac we can either pump the loo direct to sea, pump to the tank and then, by tripping the other diverter, empty the tank to sea. In my experience, dockside pumpout facilities are by no means widely available and it would be wise to be independent in that area.
 
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