Hidden basin pedastal waste

[B1N9S]

Hi,

I am fitting a new bathroom and don't want to see the waste pipe coming from the basin and I don't want to have to box it in either, as the room will be quite clinical and uncluttered looking. (Well thats the idea anyway) until the Mrs leaves 30 dozen empty shampoo bottles around (why do they do that ??).

Is it acceptable to run it stright into the floor void, across (under the floor)about 600mm to under the bath and pop it back up to tee it onto a 40mm pipe along with the bath.

As far as I can see, this would effectively be a large U bend !! Am I right in thinking that as long as I have enough of a head at the input and the outlet is lower down, then it should not back up to the sink ?? I also plan on fitting a proper pedastal trap.

 

[seco services]

Is it acceptable to run it stright into the floor void, across (under the floor)about 600mm to under the bath and pop it back up to tee it onto a 40mm pipe along with the bath.

No cause the waste pipe needs to discharge all the water.
Your idea will cause it to hold water.

 

[B1N9S]

Thanks.

So theoretically possible, but not a good idea !!!

Any reason why all the water needs to be discharged ? The trap holds water all the time, is that not the same thing ?

I am not questioning your advice, I will be following it, but just curious why !!

 

[cajar]

Not sure what pressure would be required to discharge the water in a u bend that size. Pretty sure that because traps are quite small the pressure required to discharge them is always less than the pressure of the volume of water in the pipe above it. IE you might get it coming up through the sink. You could try an experiment if you have some spare waste pipe of course - fit it together in the garden, pour a jug into it and see if it clears or backs up (and let us know the answer)

 

[45yearsagasman]

There may be other technical reasons why not to do it, but the stagnant water held in the underfloor pipe will, in time cause the pipe to block as the trap does now from time to time. Easier to clear a blocked trap than a length of pipe underfloor.
Your idea would work however. Interesting to know what would happen when you empty the bath. If in doubt,don't.

 

[B1N9S]

Thanks for the replies.

I have experimented in the garden but only with a hose, which has far more pressure than an emptying basin !!!

45year... Has hit it on the head I think. I guess over a long time the pipe could become blocked, which would be a major pain in the rectum !!!

Sounds like not such a good idea. Any other suggestions on the best and tidiest way to avoid unsightly pipework and boxing in !!!

 

[seco services]

Any reason why all the water needs to be discharged ?

Thats why waste pipes should have a degree of fall useally about 1:40
so they don't hold water. No waste pipe should hold water
Traps are ment to hold water to stop smells etc comimg back up the waste.

Any other suggestions on the best and tidiest way to avoid unsightly pipework and boxing in

Can you not have another boss on the soil stack below floor to take it straight into ?

Another reason why it maybe above the floor level is that the floor joists are in the way.
You can't go knotching 32mm chunks out of your joists to lay the pipe across.

 

[expertgasman]

Also, if you have to disconnect the pipe under the floor, you're gonna get wet................