vacuum toilets

[py_megapixel]

Perhaps less of a high-brow topic than is common on this forum, but it's a question I've had for a while, so here goes...

Many more modern train toilets come the warning "do not operate flush while seated". Pendolinos even go so far as to place the flush button behind the lid, such that it is impossible to do so.

But what happens if you do flush while seated? What is the reason for these warnings?

 

[SargeNpton]

Legend has it that if you flush whilst seated you become stuck to the seat. Another legend has it that ladies have suffered internal injuries as a result.

 

[hexagon789]

Perhaps less of a high-brow topic than is common on this forum, but it's a question I've had for a while, so here goes...

Many more modern train toilets come the warning "do not operate flush while seated". Pendolinos even go so far as to place the flush button behind the lid, such that it is impossible to do so.

But what happens if you do flush while seated? What is the reason for these warnings?

I don't know whether it would necessarily happen, but in Around the World in 80 Days, Michael Palin writes of being told an anecdote by a member of staff on board the Desert Wind of a woman who became stuck on a vacuum toilet on another service because of the flushing system. The train had to be stopped and the entire electrical system switched off before staff could free her.

Now whether that was a true story or not I don't know, but that would be the worst I could imagine happening, put it that way.

 

[37057]

More realistically you'd probably experience some splash back if the bog is a little worn out.

 

[superjohn]

Pendolinos even go so far as to place the flush button behind the lid, such that it is impossible to do so.

I always understood that was due to the flush being more effective at clearing the bowl if the lid is closed.

The other stories sound like urban myths to me. There is a gap between the seat and the bowl, making it impossible to be ‘sealed’ onto it by the vacuum.

 

[kermit]

I've never dared go in to one of those French "Autoloos", for reasons similar to the dire imaginings indicated here. Show me a machine that never, ever goes wrong!!

 

[a_c_skinner]

Pendolinos even go so far as to place the flush button behind the lid, such that it is impossible to do so.

I now feel really stupid having not worked out this was why.

 

[Scouse77]

Your entrails get sucked out on to the rails.

 

[LowLevel]

It might splash you.

There have been a small amount of verifiable cases where malfunction or human error (by staff) has resulted in the contents of the tank being voided via the pan causing a most unpleasant mess. I personally am never anywhere near the bog when it flushes.

 

[mpthomson]

I don't know whether it would necessarily happen, but in Around the World in 80 Days, Michael Palin writes of being told an anecdote by a member of staff on board the Desert Wind of a woman who became stuck on a vacuum toilet on another service because of the flushing system. The train had to be stopped and the entire electrical system switched off before staff could free her.

Now whether that was a true story or not I don't know, but that would be the worst I could imagine happening, put it that way.

It's one of those stories alleged to have happened on every airline and cruise line going, except it's never happened anywhere;

https://www.snopes.com/fact-check/stuck-on-you/

Theoretically there's a very small chance that it could cause injury but there are no recorded examples of it having done so.

 

[Starmill]

It's always most courteous to the people who use the loo after you to close the lid (assuming one is actually provided of course...) before flushing, in toilets on trains and elsewhere, because it reduces the aerosolisation of waste.

 

[trebor79]

It's one of those stories alleged to have happened on every airline and cruise line going, except it's never happened anywhere;

https://www.snopes.com/fact-check/stuck-on-you/

Theoretically there's a very small chance that it could cause injury but there are no recorded examples of it having done so.

I believe that particular urban legend has its roots in reality.
The heads on some naval craft, in particular submarines, used compressed air to force the contents overboard. If the levers were operated on the wrong order, it could result in the user "getting his own back".
It's difficult to imagine how a vacuum system, as fitted to trains and planes, could possibly result in material going the wrong way.

 

[TheEdge]

It's difficult to imagine how a vacuum system, as fitted to trains and planes, could possibly result in material going the wrong way.

I'm sure I've heard it mentioned they have a reverse flush maintenance option where the compressed air normally used to suck is used to blow to try and shift blockages.

 

[py_megapixel]

I now feel really stupid having not worked out this was why.

I don't know for a fact that this is true; it's simply my presumption, as it stands to reason and I can't see any other reason to design it like that!

 

[skyhigh]

I'm sure I've heard it mentioned they have a reverse flush maintenance option where the compressed air normally used to suck is used to blow to try and shift blockages.

The units I sign 100% do have this function.

 

[trebor79]

I'm sure I've heard it mentioned they have a reverse flush maintenance option where the compressed air normally used to suck is used to blow to try and shift blockages.

The units I sign 100% do have this function.

Crikey, wouldn't want to have to clear up the resultant mess!
So unless it's been left in some weird maintenance "unblocking" mode there's little chance of an ordinary punter getting closely aquainted with the contents of the bowl.

 

[mpthomson]

I believe that particular urban legend has its roots in reality.
The heads on some naval craft, in particular submarines, used compressed air to force the contents overboard. If the levers were operated on the wrong order, it could result in the user "getting his own back".
It's difficult to imagine how a vacuum system, as fitted to trains and planes, could possibly result in material going the wrong way.

Indeed. Maritime toilets, with their combination of levers, are very different in terms of user functionality from a standard airline or train toilet. There's very little risk of a normal customer making those toilets blow rather than suck.

Slightly OT there's a story of a Royal Marines officer in the Falklands using a toilet in a small settlement near the sea when a large wave came in and cleared the toilet the wrong way!

 

[Trackman]

I believe that particular urban legend has its roots in reality.
The heads on some naval craft, in particular submarines, used compressed air to force the contents overboard. If the levers were operated on the wrong order, it could result in the user "getting his own back".
It's difficult to imagine how a vacuum system, as fitted to trains and planes, could possibly result in material going the wrong way.

I remember reading about a u-boat being sunk because the toilet wasn’t operated correctly.

 

[TheEdge]

Crikey, wouldn't want to have to clear up the resultant mess!
So unless it's been left in some weird maintenance "unblocking" mode there's little chance of an ordinary punter getting closely aquainted with the contents of the bowl.

My vague recollection of it on 170s was you had to close the lid, then open the outside wall of the toilet to find the switch that would do a single reverse flush. Its not like you could leave it in reverse and then some poor person in the bog press flush and receive a face full.

 

[py_megapixel]

My vague recollection of it on 170s was you had to close the lid, then open the outside wall of the toilet to find the switch that would do a single reverse flush. Its not like you could leave it in reverse and then some poor person in the bog press flush and receive a face full.

I'd hope it wouldn't be a face full unless they had some unorthodox use for the toilet...

 

[hexagon789]

I remember reading about a u-boat being sunk because the toilet wasn’t operated correctly.

I remember hearing about that as well, I think that instead of getting the crew member entrusted with the job of operating the mechanism to do so, the captain tried to do it himself and flooded the boat.

 

[Devonian]

There is at least one instance of a passenger coming into closer contact with a train's vacuum plumbing than might be desirable: a French man who attempted to retrieve his mobile phone ended up being removed from a TGV whilst still attached to the lavatory. https://www.telegraph.co.uk/news/ne...-train-after-getting-arm-stuck-in-toilet.html

 

[Peter Mugridge]

Crikey, wouldn't want to have to clear up the resultant mess!
So unless it's been left in some weird maintenance "unblocking" mode there's little chance of an ordinary punter getting closely acquainted with the contents of the bowl.

When the Mk4s were first introduced, they had to have a speed restriction applied through the tunnels near Grantham after discovering the hard way that the one way discharge valves in the retention tank could be overpowered by the air pressure in the tunnels, resulting in what was termed the "waterspout effect".

Fortunately, if I remember properly, this was discovered on test and stronger valves were installed prior to service entry.

 

[DarloRich]

I have flushed these toilets while sat on them. No issue.

I remember reading about a u-boat being sunk because the toilet wasn’t operated correctly.

USS Scorpion was lost with all hands in 1968 for reasons unknown . One potential cause was the incorrect use of a"trash disposal unit"

 

[trebor79]

When the Mk4s were first introduced, they had to have a speed restriction applied through the tunnels near Grantham after discovering the hard way that the one way discharge valves in the retention tank could be overpowered by the air pressure in the tunnels, resulting in what was termed the "waterspout effect".

Fortunately, if I remember properly, this was discovered on test and stronger valves were installed prior to service entry.

Nice, I can remember seeing the retention tanks overflowing when non-stop trains passed through Durham, on a sharpish curve.
When I was a volunteer on a minor league preserved railway, the manager was ex-BR and had been involved in testing the Mk4s, he had some interesting tales.

 

[Gloster]

I remember reading about a u-boat being sunk because the toilet wasn’t operated correctly.

It was U-1206, although it is often given - even in respected sources - as U-120.