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Pressurised Thetford cassette


blackrose

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So far after a couple of months of use I'm quite pleased with my new Thetford cassette toilet, particularly since solving the dump through smelly headspace displacement issue by means of a bilge blower sucking the air out of the cassette through the cassette venting mechanism mainly used by caravanners.

 

The Thetford cassette is cleaner to empty than my old Vacuflush cassettes and they appear not to leak at all if you're reasonably gentle with them despite the poo flap looking a bit flimsy. Or perhaps that's only the case while the cassettes are new, I don't know. 

 

Anyway, all well and good until today when I changed a cassette and put an empty one into the toilet. I wanted to put a couple of litres of water in but I couldn't understand why the poo flap handle was so stiff, so I opened the lid of the toilet to have a look. When the flap did open a pressurised aerosol of smelly water sprayed up and hit me in the face. Most unpleasant!

 

I suppose it's obvious really, in these temperatures the air inside the sealed cassette expands and when it's opened it will evacuate rapidly. But the veteran Thetford users kept that one quiet when we were talking about them recently! 🤣. Is it a widely known phenomenon with these cassettes? What do you do, just remember to keep the lid closed when opening the flap in hot weather? 

 

I've had shower, chucked a load of clothes that I'd just washed back into the machine as they were hanging above the toilet and wiped over all bathroom surfaces in the vicinity. Not that I can see anything, it's just I don't like the idea of a thin film of diluted shit water all over my bathroom. 

Edited by blackrose
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2 minutes ago, blackrose said:

So far after a couple of months of use I'm quite pleased with my new Thetford cassette toilet, particularly since solving the dump through smelly headspace displacement issue by meals of a bilge blower sucking the air out of the cassette through the cassette venting mechanism mainly used by caravanners.

 

The Thetford cassette is cleaner to empty than my old Vacuflush cassettes and they appear not to leak at all if you're reasonably gentle with them despite the poo flap looking a bit flimsy. Or perhaps that's only the case while the cassettes are new, I don't know. 

 

Anyway, all well and good until today when I changed a cassette and put an empty one into the toilet. I wanted to put a couple of litres of water in but I couldn't understand why the poo flap handle was so stiff, so I opened the lid of the toilet to have a look. When it did open a pressurized aerosol of smelly water sprayed up and hit me in the face. Most unpleasant!

 

I suppose it's obvious really, in these temperatures the air inside the sealed cassette expands and when it's opened it will evacuate rapidly. But the veteran Thetford users kept that one quiet when we were talking about them recently! 🤣. Is it a widely known phenomenon with these cassettes? What do you do, just remember to keep the lid closed when opening the flap in hot weather? 

 

I've chucked a load of clothes that I'd just washed back into the machine as they were hanging above the toilet and wiped over all bathroom surfaces in the vicinity. Not that I can see anything, it's just I don't like the idea of a thin film of diluted shit water all over my bathroom. 

 

Never ever had this on ours. Even in temps of high thirties low foutries in Southern France and Italy.

 

So the reason I didnt mention it was because Ive never experienced it.

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I wonder why it's happened to me? Is it because my cassettes are brand new and well sealed? Perhaps they begin to become less airtight after a bit of use and yours weren't brand new when you've changed them in hot weather? Can't think of any other reason. 

Edited by blackrose
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Just now, blackrose said:

I wonder why it's happened to me? Is it because my cassettes are brand new and well sealed? Perhaps they begin to become less airtight after a bit of use and yours weren't brand new when you've changed them in hot weather? Can't think of any other reason. 

 

From the manual.

 

 

Screenshot_20220617-203525_Chrome.jpg

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Just press the vent button  on the top of the cassette before insertion, on mine its  yellow, there is also the auto vent that can be pressed .  Only open the flap with the lid down ;)

 

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32 minutes ago, blackrose said:

I wonder why it's happened to me? Is it because my cassettes are brand new and well sealed? Perhaps they begin to become less airtight after a bit of use and yours weren't brand new when you've changed them in hot weather? Can't think of any other reason. 

If it makes you feel any better I had the same happen to me with your neighbours loo the other day. Least yours was your own 😀

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29 minutes ago, Loddon said:

Just press the vent button  on the top of the cassette before insertion, on mine its  yellow, there is also the auto vent that can be pressed .  Only open the flap with the lid down ;)

 

 

The funny thing is that I have the plastic plate fitted in the bottom of the toilet below the cassette to activate the auto vent but that didn't seem to release the pressure.

 

Where does the cassette vent out to if you push the yellow vent button? 

Edited by blackrose
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10 minutes ago, blackrose said:

Where does the cassette vent out to if you push the yellow vent button

Around the button. Its designed to let air in when you empty the cassette so presumably will let air out when there is excess pressure inside.

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28 minutes ago, blackrose said:

 

The funny thing is that I have the plastic plate fitted in the bottom of the toilet below the cassette to activate the auto vent but that didn't seem to release the pressure.

 

Where does the cassette vent out to if you push the yellow vent button? 

It sounds like there is a malfunction on the auto vent (the gismo on the top to the left of the handle and slider). Whether the malfunction is on the cassette or the toilet I don't know, but I've never had to release the pressure from the yellow button, I only use that when emptying the cassette to stop it air locking.

 

image.png.30000b6ff28d92836e4adbdf6061e525.png

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23 minutes ago, Wanderer Vagabond said:

It sounds like there is a malfunction on the auto vent (the gismo on the top to the left of the handle and slider). Whether the malfunction is on the cassette or the toilet I don't know, but I've never had to release the pressure from the yellow button, I only use that when emptying the cassette to stop it air locking.

 

image.png.30000b6ff28d92836e4adbdf6061e525.png

The auto vent won't vent excess pressure: the mechanism holds it closed when not inserted into a toilet, but doesn't positively open it when activated. That's because to can be closed by a float when the cassette is full. That lifts a rubber flap which seals the vent. If the flap is closed and positive pressure builds up in the cassette, that will hold the rubber flap in the sealed position. The yellow vent button is the best way to release any excess pressure. 

 

MP.

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I think I encountered this phenomenon once after loading my spare cassette that I store in the engine bay, so it was quite warm. I opened the flap and there was a small release of pressure but it didn't hit me. I made a mental note to only open the flap when the seat is down and never to peer closely at the flap when opening it! 

 

You have to remember that these toilets are designed for caravan/motorhomes where a single cassette is in use. It gets full, then emptied, then put back in the toilet right away. Having a spare cassette stored for long periods was not envisaged by the designers. I always put the couple of litres of water and blue in at the Elsan, before I store the cassette to save messing with it when I come to use it. 

Edited by booke23
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Yes. They do. Keep the lid down and pull out the slide to reduce the pressure.

 We know all about this one because our loo is in the engine room ( only place) and the boat has an air cooled engine. Great for drying clothes , not so great for assisting the loo.

Our cassette can get quite um bloated and therefore does what most bloated things do.

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15 hours ago, booke23 said:

 

You have to remember that these toilets are designed for caravan/motorhomes where a single cassette is in use. It gets full, then emptied, then put back in the toilet right away. Having a spare cassette stored for long periods was not envisaged by the designers. I always put the couple of litres of water and blue in at the Elsan, before I store the cassette to save messing with it when I come to use it. 

 

What makes you think that caravanners don't carry spare cassettes? I'd have thought plenty do as they often park up where there are no facilities, but I have no direct experience of motorhomes and caravans so I might be wrong. 

 

However, whether one puts the water and toilet fluid into a cassette directly after emptying it or before using it all amounts to the same thing. You just mess with it earlier. 

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1 minute ago, blackrose said:

 

What makes you think that caravanners don't carry spare cassettes? I'd have thought plenty do as they often park up where there are no facilities, but I have no direct experience of motorhomes and caravans so I might be wrong. 

 

However, whether one puts the water and toilet fluid into a cassette directly after emptying it or before using it all amounts to the same thing. You just mess with it earlier. 

 

We carried one for a while but found there was no real benefit in doing so as we dont 'wild camp'. It became just something else to store and get in the way.

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2 hours ago, roland elsdon said:

Yes. They do. Keep the lid down and pull out the slide to reduce the pressure.

 

 

Well now I know for future reference. The only reason I had the toilet lid up and was looking at the flap was because I couldn't understand why the flap lever had become stiff. Obviously the flap was being held in place by the excess pressure inside the cassette but I hadn't realised. 

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23 minutes ago, blackrose said:

 

Well now I know for future reference. The only reason I had the toilet lid up and was looking at the flap was because I couldn't understand why the flap lever had become stiff. Obviously the flap was being held in place by the excess pressure inside the cassette but I hadn't realised. 

 

Its worth giving the flap/seal an occasional spray with some silicone spray. 

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44 minutes ago, blackrose said:

 

What makes you think that caravanners don't carry spare cassettes? I'd have thought plenty do as they often park up where there are no facilities, but I have no direct experience of motorhomes and caravans so I might be wrong. 

 

I've done a bit of motorhoming and caravanning, and I've never seen anyone do it. There's just no point in carrying a spare cassette when you use campsites. Especially as space is at even more of a premium on a motorhome/caravan compared to a narrowboat. 

 

44 minutes ago, blackrose said:

However, whether one puts the water and toilet fluid into a cassette directly after emptying it or before using it all amounts to the same thing. You just mess with it earlier. 

 

Well you then mess with it twice. I prefer to do all the messing in one go!

 

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47 minutes ago, blackrose said:

whether one puts the water and toilet fluid into a cassette directly after emptying it or before using it all amounts to the same thing. You just mess with it earlier. 

I just tip a cap full of bio washing liquid in once the cassette is in place, never add extra water as it just takes up room that could otherwise be used. Its not messy ;)

 

 

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2 hours ago, booke23 said:

 

Well you then mess with it twice. I prefer to do all the messing in one go!

 

 

My point was just that you spend the same amount of time putting fluid in the cassette whenever you do it. It's really not that big a deal pouring a cap full of liquid in and flushing the toilet. 

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10 minutes ago, blackrose said:

 

My point was just that you spend the same amount of time putting fluid in the cassette whenever you do it. It's really not that big a deal pouring a cap full of liquid in and flushing the toilet. 

 

You're not putting additives in via the bowl are you? That's a recipe to damage the lip seal of the flap. From the manual:

 

image.png.30ff13ae0f6b987b82419d0c92a35727.png

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4 minutes ago, booke23 said:

 

You're not putting additives in via the bowl are you? That's a recipe to damage the lip seal of the flap. From the manual:

 

image.png.30ff13ae0f6b987b82419d0c92a35727.png

 

I was just about to ask the same. You beat me to it.

 

You can do it if you are very careful (I have on occasions) but its not recommended.

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8 minutes ago, The Happy Nomad said:

You can do it if you are very careful (I have on occasions) but its not recommended.

 

Yes I've done it once, when I wanted to top up the quantity of blue on a half full tank. Like you say it requires great care so that the blue pours straight in without touching the sides. If I did it habitually, it would definitely touch the sides and seal at some point.

I've been meaning to get some of those blue sachets for this very purpose, you could safely throw those in all day long and not contaminate the seal I imagine. 

Edited by booke23
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15 minutes ago, booke23 said:

 

Yes I've done it once, when I wanted to top up the quantity of blue on a half full tank. Like you say it requires great care so that the blue pours straight in without touching the sides. If I did it habitually, it would definitely touch the sides and seal at some point.

I've been meaning to get some of those blue sachets for this very purpose, you could safely throw those in all day long and not contaminate the seal I imagine. 

I would avoid the sachets, I bought some once and in the heat the box of sachets became a sticky mess as everything sort of melted into one big lump of blue crystals and sachet.

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