[[File:Jet cleaning.jpg|thumb|Diagram of hydrojetting cleaning apparatus]]
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To permit access by cameras or cleaning apparatus, 90 degree connector must not be used in underdrains. Instead 2 x 45 degree couplers, or preferably 3 x 30 degree couplers should be used instead. For the same reason, dual walled perforated pipes with smooth internal walls are necessary.
*[[Wells]], of 100 - 150 mm diameter perforated pipe, should extend to the bottom of the facility.
*[[Wells]], of 100 - 150 mm diameter perforated pipe, should extend to the bottom of the facility.
*The exposed tops of all wells should be fitted with lockable caps.
*The exposed tops of all wells should be fitted with lockable caps.