Toilet Waste Tank

[Ray]

Hi. I'm about to place an order for the dump through toilet waste tank for our sailaway. We have a preferred size which should give us about 105 litres capacity. However, we can increase this size by robbing some of the storage space under the bed and/or by increasing the height of the toilet above the cabin floor which makes things a bit uncomfortable for the shorter female crew members. Ideally, we'd like to be able to go for about 2 weeks betwen pump outs when there's just the two of us on board (and cruising).

 

Does anyone have any idea of the average (normal) usage as measured in litres per person per day? We think we have an average liquid intake

 

Thanks

[CampinGazz]

When i was on my own, my thetford cassette tank (17 litres totaly full, 15 litres to warning light) could last me a week easily,

 

now i'm with my other half, we tend to last 3 days, tho we both have colitis, and sometimes we can fill it in a day.

 

BUT, we are in a motorhome, and it seems that motorhomes use a lot less water than a boat does, 140 litres of water lasts us a week easily,

i've heard some boats struggle to go a week on 140 gallons (and we do have a washing machine in the motorhome, shower, kitchen and bathroom sink, toilet flush, and the outside hose point for washing the dog off when she's been rooting out the muddiest place to go for a roll in etc)

 

You could alwyas do it the scientific way, measure everything, that's how i worked out the pump, pipe and shower head size to get a good shower in my van, measured the pressure of the house water and flow at the shower head i wanted to replicate in the van,

 

also worked out the fresh and grey water tank capacities to last us a week by measuring a day's water usage,

 

the toilet we had no say in, as it was 17 the litre tank that came with it, or a hole through the floor

i'd have liked one of the 70's incinerator attatchments american RV's used to have, as you drove along every few minutes set ammount of waste from the holding tank was sent into the engines exhaust just after the manifold,

little puff of smoke from the tail pipe, and that was it, no need to dump the tanks as long as you drove over a certian speed (to get the exhaust pipes hot enough) every so often,

[Theo]

i'd have liked one of the 70's incinerator attatchments american RV's used to have, as you drove along every few minutes set ammount of waste from the holding tank was sent into the engines exhaust just after the manifold,

little puff of smoke from the tail pipe, and that was it, no need to dump the tanks as long as you drove over a certian speed (to get the exhaust pipes hot enough) every so often,

 

 

That seems a good idea. It would be good if you could get one for a boat!

 

Nick

 

Ps Would not work for Theodora, though. Wet exhaust. Very nasty!

 

Nick

Edited March 6, 2007 by Theo

[Keeping Up]

Hi. I'm about to place an order for the dump through toilet waste tank for our sailaway. We have a preferred size which should give us about 105 litres capacity. However, we can increase this size by robbing some of the storage space under the bed and/or by increasing the height of the toilet above the cabin floor which makes things a bit uncomfortable for the shorter female crew members. Ideally, we'd like to be able to go for about 2 weeks betwen pump outs when there's just the two of us on board (and cruising).

 

Does anyone have any idea of the average (normal) usage as measured in litres per person per day? We think we have an average liquid intake

 

Thanks

I'd recommend going for a slightly larger size if you can.

 

We have the same setup, with a Mansfield Traveller dump-through into the waste tank. The two of us spend about 6 months of the year cruising, and reckon we also have a fairly average liquid intake (on the days when our intake is greater, that usually implies we are probably at the pub and naturally we make as much use of their waste facilities as we can). As well as the liquid output from the people, there is a small quantity of freshwater flushed through with every usage, and the total waste works out at just a little under one gallon per person per day (to be slightly pessimistic we plan on a basis of one full gallon and hope this will give us a bit of spare capacity).

 

Our tank capacity is 35 gallons. Of course, a pump-out will never remove the last gallon or two; also you may not be passing a pumpout every day and it pays to have at least 2 days capacity to spare (and also, you really don't want to fill it to the brim because the air can't circulate properly and it will smell). So realistically we can treat our tank as about 30 gallons usable capacity, so it would last two people about 15 days. And that is what we find in practice. If we're extremely careful and make a lot of use of the on-shore facilities we may just about stretch it to 3 weeks before it's full to the brim but it's not wise to count on that. We do keep a small PortaPotti in the cupboard just in case. It probably gets used on one or two occasions a year.

 

I always think in gallons but in litres the above would be saying we have a 150 litre tank of which we can only use about 130, and you should allow for at least 4 litres per person per day.

 

How deep is your tank? Ours is about 9 inches and Debbie is quite short, she finds that OK to use. You could always provide a footrest.

 

Allan

[blackrose]

Hi. I'm about to place an order for the dump through toilet waste tank for our sailaway. We have a preferred size which should give us about 105 litres capacity. However, we can increase this size by robbing some of the storage space under the bed and/or by increasing the height of the toilet above the cabin floor which makes things a bit uncomfortable for the shorter female crew members. Ideally, we'd like to be able to go for about 2 weeks betwen pump outs when there's just the two of us on board (and cruising).

 

Does anyone have any idea of the average (normal) usage as measured in litres per person per day? We think we have an average liquid intake

 

Thanks

 

This is off topic slightly, but as you mentioned making things uncomfortable for crew members I wondered why you are going for a dump through?

 

In most systems the vent from the tank outside the boat releases the build up of gasses while the toilet is not in use. However, whilst in use whatever waste goes into a tank the same volume of putrid gas has to get out, and for many dump throughs the path of least resistance for gasses to escape from of a tank is often straight up through the toilet and into the boat.

 

If it's made more difficult for these gasses to pass up through the toilet then they will exit via the vent. If the pipework is correctly installed a remote tank facilitates this because the gas can't travel through water held in a U bend for example, even if the remote tank is just offset to one side.

 

I know some people will say their dump through doesn't smell so I guess either the toiltet must have a very quick closing mechanism or there is something else I haven't taken into account (perhaps their sh*t don't stink ), but anyone hiring for a week shouldn't necessarilly conclude that dump throughs don't smell. These hire boat tanks get pumped & flushed out on a regular basis and in liveaboard use you might not be emptying it quite as much.

Edited March 7, 2007 by blackrose

[ChrisPy]

... or a hole through the floor

that would resolve a lot of problems. why didn't I think of it ?

[charles123]

You should go for a much bigger tank in my opinion since yours is quite small, you will be forking out £15 to empty it frequently.

 

Your proposed tank is no bigger than 22" x 22" x 12"

 

If you assume .8 litre of waste/water every time used this gives 113 flushes at 8 times used per day gives you 14 days to fill the tank, so your requirement of going 2 weeks between emptying does work out according to me

 

If you can afford it a macerator toilet will give you house quality facilities and is well worth the investment

 

To give you the same number of days between pump outs the calculation is a tank size 30" x 30" x 12" for a macerator

 

All number approximate

 

Charles

[Ernie]

I agree with Charles, go for the biggest tank you can fit in order to save on pump out charges.

 

If you do go for a BIG tank, remember to fit it as close to the centre line of the boat as you can so that it doesn't effect the levelling of the boat as it fills.

 

I have a Tecma macerator feeding into a big tank (about 35x30x12 inches) and am very happy with it. I tend to empty it as soon as it gets about 50-75% full so that I never get into a panic situation. I also carry a Thetford as an emergency backup.

[Tony Brooks]

This is off topic slightly, but as you mentioned making things uncomfortable for crew members I wondered why you are going for a dump through?

 

In most systems the vent from the tank outside the boat releases the build up of gasses while the toilet is not in use. However, whilst in use whatever waste goes into a tank the same volume of putrid gas has to get out, and for many dump throughs the path of least resistance for gasses to escape from of a tank is often straight up through the toilet and into the boat.

 

If it's made more difficult for these gasses to pass up through the toilet then they will exit via the vent. If the pipework is correctly installed a remote tank facilitates this because the gas can't travel through water held in a U bend for example, even if the remote tank is just offset to one side.

 

I know some people will say their dump through doesn't smell so I guess either the toiltet must have a very quick closing mechanism or there is something else I haven't taken into account (perhaps their sh*t don't stink ), but anyone hiring for a week shouldn't necessarilly conclude that dump throughs don't smell. These hire boat tanks get pumped & flushed out on a regular basis and in liveaboard use you might not be emptying it quite as much.

 

 

I think this mis-states the correct operation of any holding tank.

 

AS long as you can ensure adequate fresh air (ventilation) across the surface of the tank the aerobic bacteria in the effluent will break down the stuff with very little smell indeed. If you restrict amount of air across across the top of the tank the aerobic bacteria die and anaerobic ones thrive. These are the ones that cause smell when they anaerobically break down the effluent.

 

Ensure (as far as you can) aerobic decomposition and you will get very little smell indeed.

 

The trouble is that far too many builders fit totally inadequate breathers and far too many people with adequate breathers use blue to try to preserve the turds. Blue kills bacteria and anaerobic ones are hardier than the aerobic ones - hence smell.

 

My answer to the original questions would be go for the largest tank you can sensibly accommodate and fit at least a 32mm breather at each end. If any breather pipes have top be more than a couple of feet long or need many elbows fit a brushless computer fan in one breather pipe. Mine is operated by a pneumatic timer switch in the loo.

 

Since fitting a 32mm breather in addition to the stupid 3/8" one fitted by the builder plus fan we do not get much smell inside the boat. Most of the time there is no smell - even if I forget to push the button. Sometimes in summer there is a slight smell upon the first "opening" when we return to the boat after a week or so away, but its OK on subsequent uses.

 

In high summer we do get a smell outside the boat after at least three weeks without a pump out and continual use. However this smell is more like muddy saltmarsh than typical toilet smells.

 

If anyone wants to verify my assertions I will be happy for them to inspect the boat. Its close to the Braunston level. Email privately to arrange.

 

Tony Brooks

[blackrose]

I think this mis-states the correct operation of any holding tank.

 

AS long as you can ensure adequate fresh air (ventilation) across the surface of the tank the aerobic bacteria in the effluent will break down the stuff with very little smell indeed. If you restrict amount of air across across the top of the tank the aerobic bacteria die and anaerobic ones thrive. These are the ones that cause smell when they anaerobically break down the effluent.

 

Ensure (as far as you can) aerobic decomposition and you will get very little smell indeed.

 

The trouble is that far too many builders fit totally inadequate breathers and far too many people with adequate breathers use blue to try to preserve the turds. Blue kills bacteria and anaerobic ones are hardier than the aerobic ones - hence smell.

 

I disagree. Aerobic decomposition will only occur at the surface and anerobic bacteria will continue to thrive in the anerobic conditions underneath the surface of the waste whether there is air above or not. Their by-products will rise and escape through the vent until the dump through is opened and there is less pressure to escape through the toilet. In addition, when you have a dump into a dump through there may be displacement created not only in the air but also in the waste, which forces these anerobic gasses to rise

Edited March 7, 2007 by blackrose

[anhar]

Slightly but this product, BioMagic, is claimed to be far superior to blues in ridding all kinds of boat toilets etc. from odours by speeding up decomposition using the bacteria already present in the waste.

 

Can't vouch for it myself though, yet. I expect it to be using it on my new boat to be delivered in a couple months.

 

http://www.biomagicuk.com/2.html

 

regards

Steve

Edited March 7, 2007 by anhar

[CLIVE AND JUDY]

We have just started using Bio Magic. Does just what it says on the tin - no smell.

Will have to wait and see if its as good in the summer.

It seems expensive, but you don't use much. The guy where we got ours (in Bradford on Avon) said not to use any more than they suggest as it defeats the object, whatever that means!

[Ray]

Many thanks for all the responses.

 

After 20 odd years working with trip and hire boats on a very part time basis, I planned to go for the biggest tank I could fit. My problem is that, even with a 57ft boat, space is at a premium and I'd prefer not to encroach upon the bedroom if I can avoid it.

 

I've contemplated removing the floor and the relevant part of the supporting bearer and levelling the slab ballast to the cross steelwork height and resting the tank on that. That would give us about another 60mm. We have the inevitable bulkhead behind the loo and then a small service area, about 75mm wide to hide the pipework from the wash basin. We could eat into that service area below the pipework to give us a bit more (front to back) depth but I'd only want to do this in the middle of the tank - which is across the bathroom - to enable us to continue to support the bulkhead on both edges and also so that we can get to the pipework joints for the wash basin water and waste if we need to - the boat is being fitted out to be as maintenance friendly as possible.

 

If push comes to shove I can encroach slightly on the bedroom but as this is our main storage area for clothes and bedding, we want to minimise any space loss.

 

My own calculations were that approx 5 litres per day should be sufficient per person, so we'd get 10 days out of our initial tank size. We kind of confirmed our calculations by working out that we normally drink about 4 pints of tea a day - just over 2 litres. Throw in some soup and some solids that will need to be disposed of, and 5 litres seemed adequate. However, having just spoken to someone who runs a couple of hire boats, he reckons that their average returns, so to speak, indicate that they need to provide for 15 gallons per person per week - that's nearly 70 litres per person per week, 10 litres per day!

 

We've gone down the dump through path to minimise the amount of extra water that the tank has to accept. In all my time working on trip boats, the only smells that we get tend to be those from the area immediately around the toilet and not from the tank!

 

The boss says that she can cope with a loo with the base 30cm off the floor but she has to sit with only her toes on the floor.

 

I'll have a look at Bio Magic once the tank gets here and the second vent and fan seem good ideas.

[David Schweizer]

I have just removed the Mansfield Traveller and holding tank from my boat. The tank was 12"x22" x48" with a capacity of about 200 litres. With the two of us on board it seemed to last all summer before needing a pump out, but the smell was so awful after a month or so, that we had to empty it when it was less than half full. We have been using a Porta Potti (plus spare tank) for the last seven years and have decided that we do not need the dump through, so it has gone, prioviding some much needed extra storage space. I did offer it free to anyone on this forum, but there were no takers.

Edited March 9, 2007 by David Schweizer

[Keeping Up]

My own calculations were that approx 5 litres per day should be sufficient per person, so we'd get 10 days out of our initial tank size. We kind of confirmed our calculations by working out that we normally drink about 4 pints of tea a day - just over 2 litres. Throw in some soup and some solids that will need to be disposed of, and 5 litres seemed adequate. However, having just spoken to someone who runs a couple of hire boats, he reckons that their average returns, so to speak, indicate that they need to provide for 15 gallons per person per week - that's nearly 70 litres per person per week, 10 litres per day!

 

We've gone down the dump through path to minimise the amount of extra water that the tank has to accept. In all my time working on trip boats, the only smells that we get tend to be those from the area immediately around the toilet and not from the tank!

I think you'll find that 5 litres a day is fine; as I said in my post above that is the figure we've calculated from many years of boating. The difference probably is that many of the people on hire boats are not used to boating, so they're not used to the idea of economising on the use of the on-board facilities. Plus if they are a family, the new loo is such a fascination for the kids that they just have to keep going.

 

We always find that when we have guests on board, they contribute far more than their fair share to the contents of the tank; a typical scenario is where they use the toilet every time just before leaving the boat, as they would probably do when leaving their own home, even when you have just moored up outside the pub which you are about to visit. As boaters it becomes second nature to wait until you are in the pub, and to use their facilities again just before returning to the boat.

 

When our boat was first built the dump-through used to smell once it reached half-full. This was without doubt because the vent was too small; when we had it increased (to the same size as the pump-out) the smell totally disappeared. We can let the tank get to within about an inch of the top before the smell returns - except on extremely windy days when the wind can blow into the vent and provide you with a waft of smell when yuo open the trapdoor. We don't use blue, but have a sort of yeast compound designed for farmers' septic tanks, and it seems to work very well; if you ever do put blue in the tank, it would take several flushes to get rid of it if you did want to change to any such bio-digestive alternative.

 

Allan