gradients on toilet waste

[medsok]

I'm fitting a 'back to wall' toilet but the main soil pipe runs at 90deg. to it for 1.3mtr under cabinets before it drops into the main downpipe. Do i need to have a gradient?

 

[seco services]

i would on that distance.

 

[Elkato531]

Minimum gradient on soil and waste pipework should be 1 in 40 or 25mm per metre. With smaller flush volumes of modern WCs its even more important to have the correct fall.