drainage too the septic tank Drainage and wastage systems and plumbing help, advice and answers

[david somerville]

can any one tell me if the under ground pipe has a fall of 1 in 79".
or is this wrong? someone told me that it was in the regs at 1 in 79".
but i've not read it myself.
can you help. p.s. 4" pipe is being used.

[thedrainman]

Hi

This answer has been given by another member a few days ago

DEPENDS ON THE DIAMETER OF THE PIPE AND LENGTH OF THE PIPE FROM TOILET TO WHERE IT ENTERS VIRTICAL SOIL PIPE.

WHERE THE PIPE IS FOR SEWAGE ALONE A MODERATE FALL IS BETTER THAN A STEEP ONE.
THE LIQUID SHOULD NOT RUN AWAY LEAVING DEPOSITS TO FORM AND ADHERE TO THE DRAIN.(POTENTIAL FOR BLOCKAGES).

THERE IS A RULE OF THUMB METHOD OF DETERMINING THE FALL REQUIRED.
THAT IS, MULTIPLY THE DIAMETER OF THE PIPE IN INCHES BY TEN.
THEREFORE 100mm (4") PIPE NEEDS FALL OF 1 IN 40
150mm (6") PIPE NEEDS FALL OF 1 IN 60

This is right, however do you mean the main drainage to the tank or the discharge from the tank to a soakaway in which case 1 in 80 is ok as the pipe should be purferated to allow the water to seep into the soakaway.

I hope this helps

The drainman keeping you flowing so you can keep going

[arbco]

1:79 is a possibility but the regs suggest 1:40 to 1:60 for foul as guidance. 1:80 is sometimes used but depends on the flowrate and number of appliances connected. Could someone really lay a drain to 1:79??? The B Regs nor the B Standard have never specifically stated 1:79 to my knowledge.