49 C.F.R. § 178.270-9 Inspection openings.
Title 49 - Transportation
Each portable tank must be fitted with a manhole or other inspection opening sited above the maximum liquid level to allow for complete internal inspection and adequate access for maintenance and repair of the interior. Each portable tank with a capacity of more than 1,894 L (500 gallons) must be fitted with an elliptical or round manhole at least 279 × 381 mm (11 × 15 inches), or 254 × 405 mm (10 × 16 inches), or with a circular manhole at least 381 mm (15 inches) in diameter. Any inspection opening and closure must be designed and reinforced as required by Section VIII of the ASME Code (IBR, see §171.7 of this subchapter). [68 FR 75750, Dec. 31, 2003]
Title 49: Transportation
PART 178—SPECIFICATIONS FOR PACKAGINGS
Subpart H—Specifications for Portable Tanks
§ 178.270-9 Inspection openings.