Fall rate in waste pipe

[Pepepriest]

Hope someone can help, currently have a new build property (was Kier now Tilia) 18 months old and it looks like there is no fall rate between the cloakroom toilet and the vertical waste pipe. I have checked with a spirit level and the pipe is level.
Feel free to advise on whether there should be a fall rate in this pipe as it is taking toilet waste and I fear it could block up in time.
I have spoken with Tilia and their contracted plumbers and they say it is ok which I find hard to believe.

 

[ShaunCorbs]

25mm ideally but you can get away with 15mm min but nothing less

 

[rpm]

25mm ideally but you can get away with 15mm min but nothing less

Is that per metre, over entire length or something else.

 

[Last Plumber]

If it is a 4" soil pipe running horizontal it should be 1:40 fall in my book.

 

[ShaunCorbs]

Per meter sorry

 

[oz-plumber]

Get the Plumbers whom you spoke with, to put that in writing.
Get them to stat that a level soil drain from a toilet to a stack should be ok.

As a rough guide, 1/4 of the bubble should be outside the line in the level.
So using your level, the edge of the bubble should be touching or past the second line on the high side of the drain as minimum fall.