drainage too the septic tank


Postby david somerville » Fri Mar 21, 2008 2:59 pm

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.
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Postby thedrainman » Fri Mar 21, 2008 4:38 pm

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
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Postby arbco » Fri Mar 21, 2008 8:39 pm

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.
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