Can the toilet waste water flow straight down from the trap?

[Ben100]

Hi all, I’m looking to install a toilet on the first floor of my house and I’m trying to work out the plumbing for the foul water. Can the foul water flow directly down from the toilet trap and out? Basically straight out of the toilet and through the floor. Or will this create too much pull on the trap and cause it to empty?

[PeterW]

Do you mean out of the trap and then into a vertical soil stack ..?

[ProDave]

You will need the stack pipe to rise above the level of the toilet and either vent to an outside stack or vent to an Air admittance valve.  I can't picture exactly what you are suggesting but I can't see how you can connect it without a branch and a pipe going up.

[Ben100]

Just now, PeterW said:

Do you mean out of the trap and then into a vertical soil stack ..?

Basically, yes. I want the foul water out of the upstairs bathroom ASAP, which means straight down.

[PeterW]

Ok but you will need to vent the stack - You’ll need an AAV on a stub near the WC. No issue connecting virtually directly but watch out for showers etc connecting within the same zone as the WC - you may need to drop the shower down the stack to connect. 

[Ben100]

2 minutes ago, ProDave said:

You will need the stack pipe to rise above the level of the toilet and either vent to an outside stack or vent to an Air admittance valve.  I can't picture exactly what you are suggesting but I can't see how you can connect it without a branch and a pipe going up.

So I was planning to use the 90 degree fitting off of the toilet trap to go down about 1m into the utility room below, before connecting to a gradual fall pipe already in place.

 

For venting I’m looking to install a AAV somewhere along this stretch of pipe work.

[Ben100]

2 minutes ago, PeterW said:

Ok but you will need to vent the stack - You’ll need an AAV on a stub near the WC. No issue connecting virtually directly but watch out for showers etc connecting within the same zone as the WC - you may need to drop the shower down the stack to connect. 

Ok. I’ve read that the AAV needs to be within 2m of the WC. Is this correct?

[PeterW]

7 minutes ago, Ben100 said:

So I was planning to use the 90 degree fitting off of the toilet trap to go down about 1m into the utility room below, before connecting to a gradual fall pipe already in place.

 

You will need to put a long radius bend on the bottom of the pipe and secure it properly as it will be under load as you flush down the pipe. 
 

What’s the full layout ..??

[ProDave]

10 minutes ago, Ben100 said:

So I was planning to use the 90 degree fitting off of the toilet trap to go down about 1m into the utility room below, before connecting to a gradual fall pipe already in place.

 

For venting I’m looking to install a AAV somewhere along this stretch of pipe work.

Make that a tee and then a pipe can go up to the AAV which should be 1M above the WC

[Temp]

+1  I believe the regs say the AAV must be higher than the wash basin waste?

[Ben100]

I thought the AAV just needs to be 10cm above the waste pipe? 1m above the basin is quite high!

[Nickfromwales]

If you petition your building control officer, you should get him / her to agree to a deviation. As you have less than 1300mm between inverts ( the level where the water sits in the WC pan, and the lower level of the horizontal pipe you are connecting to 1000mm below, you don’t actually need either of the above. 
I would recommend an anti-siphon trap on the basin only as a belt and braces arrangement, but ( and I have assumed this ) you’re connecting into a horizontal stack then you won’t have any issues with vacuum deficit from flushing the loo, as the drop of 1000mm and then turning to horizontal ( so then getting a full air-break at that point ) a vacuum will  it happen. 
 

Question is, what does the horizontal pipe.......

11 hours ago, Ben100 said:

a gradual fall pipe already in place.

.......service? If this goes to a bathroom then you need to ensure that adding to the soil pipe at the point you are suggesting doesn’t cause other issues. Does that terminate at a vent or air admittance valve etc? How do you intend to join to that gradual fall pipe? Replacing a bend with a T, or cutting into that existing the horizontal pipe at a mid-point? A pic of the topology would help, just scribble and snap and post it for us to give as best advice as possible.

[Ben100]

Sorry for the slow reply. I needed to install the pipe work to show what I mean!

 

As you can see, both the soil pipe and waste pipe are dropping directly down about 1m from the traps. Is this ok? And where should I install the vent? I was thinking of installing a vent pipe out to the roof, in the same length of vertical soil pipe which the waste pipe connects to.

 

 

[Ben100]

On 11/04/2021 at 21:24, PeterW said:

You will need to put a long radius bend on the bottom of the pipe and secure it properly as it will be under load as you flush down the pipe. 
 

What’s the full layout ..??

thanks. I’ve uploaded some pictures above showing the layout  ☝️

[PeterW]

That’s really not ideal... should track around the ceiling at 1:80, then when it reaches the far corner it drops down vertically. The other waste  should go into the horizontal run not that vertical drop. 
 

[Ben100]

35 minutes ago, PeterW said:

That’s really not ideal... should track around the ceiling at 1:80, then when it reaches the far corner it drops down vertically. The other waste  should go into the horizontal run not that vertical drop. 
 

Ok, what’s the reason for this way?

 

The reason I’ve installed it like this is because I didn’t want to come down by the outside wall window. Also, on the other side of the outside wall the pipe makes a 90 degree turn, so I was worried about a big fall before hitting the 90.

[markc]

The 45 degree slope and the lower one are both too steep, you risk having the solids stick in the pipe because the water will run too fast. 1:80 slope ensures the solids are carried by the water and they float along

[Ben100]

2 minutes ago, markc said:

The 45 degree slope and the lower one are both too steep, you risk having the solids stick in the pipe because the water will run too fast. 1:80 slope ensures the solids are carried by the water and they float along

Right, got it. I’ll change the 45 to a straight drop and out along the floor at a 1:80. Cheers!

[markc]

3 minutes ago, Ben100 said:

Right, got it. I’ll change the 45 to a straight drop and out along the floor at a 1:80. Cheers!

i would be careful to support the lower bend well because the fall will cause a hammer effect and could separate the fittings. also im not sure thats acceptable to have a vertical followed by horizontal inside the house.. someone else may be able to shed more light on the regs etc.

[Nickfromwales]

On 14/04/2021 at 17:02, markc said:

i would be careful to support the lower bend well because the fall will cause a hammer effect and could separate the fittings. also im not sure thats acceptable to have a vertical followed by horizontal inside the house.. someone else may be able to shed more light on the regs etc.

Nothing wrong with that, but if BRegs were eye-balling this they'd want robust access for rodding / maintenance where the adverse changes in direction were. As long as the first invert at 1000mm turns to horizontal, an air bereak will occur and there is still no need for a stub-stack or 110mm air admittance valve. Basin anti-vac will suffice.

[Nickfromwales]

Oh, and beef up the timber work for that WC frame. That ain't enough beef there me ol' china mug  

Or ban any olympic pie-eaters from that bathroom........

[Ben100]

20 hours ago, Nickfromwales said:

Oh, and beef up the timber work for that WC frame. That ain't enough beef there me ol' china mug  

Or ban any olympic pie-eaters from that bathroom........

yes, will do! ?