FlexWorks Tank Sump Mounting Flanges are used to mount tank sumps to 4" and 6" UST bung fittings. The Flange Top models provide added flexibility in the positioning of pump or extractor outlets. The No-Bolt Style mounting flange is used to mount sumps to 4" UST bung fittings and attaches to the bottom of the sump for added security and liquid-tight connection.