will this be ok to do,someone wants me to lay some 40mm wastepipe under some paving blocks for relocation of a washing machine,but to get it there,there will be a 90 degree bend from outside the house to direct the pipe toards the ground,then another 90 to direct the pipe towards a gulley,total lenght of the waste pipe will approx 3m,which will only have a fall of around 50mm ffor the whole length of the pipe,now i realise this is not enough,and the two 90 bend will restict flow further,with it being so close to the upstand pipe for the washing machine,but he has been made aware of this,and is sure it will be ok,as there is not much water that comes out a wm.