Sloped Bottom tanks are offered as both Internal and External. All Sloped Bottoms are designed in accordance with ASTM D-3299 or D-4097 standards. Internal Sloped Bottoms come standard with a 1â€ minor and bottom core to sit flat on your support pad. External Sloped Bottoms require the customer to provide a sloped support pad. Belding Tankâ€™s standard pitch is Â¼ inch per foot to allow drainage to the low side of the slope. Either bottom design requires full bottom support.