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It doesn’t matter what kind of stakes you use. Drive the stakes into the ground using a mallet or a hammer. This will help make sure you create sloped drain pipes so your tanks can empty out. Use your hammer or mallet to drive the stake down until it’s the same height as the first. Pound the second stake down until the level is balanced. The second stake is now 1 inch (2.5 cm) lower than the first, or 1⁄4 inch (0.64 cm) lower per 1 foot (30 cm). Continue adding stakes down the rest of the trench every 3 7⁄8 feet (1.2 m) from the last one so the stakes slope away from the drums. The gravel will now slope away from the drums at 1⁄4 inch (0.64 cm) per 1 foot (30 cm) of horizontal distance. Slide the ends of the drain pipes into the 45-degree bends on the lower drum. Make sure the holes in the pipes face down so liquids can soak back into the ground. Adjust the slope by adding or removing gravel under the pipe. Use a 2-part epoxy or silicone caulk for the best seal on your drain pipes. Try using flex pipe for this, so that if the ground shifts it will give a little. Bury the trench to the top of the bottom drum with the remaining gravel. This will prevent the soil from seeping into the gravel and ensure that you maintain good drainage on your tanks. Make sure the ground is level when you finish filling in the area with your soil. Leave the top pipe from the first tank exposed so you can easily access the tanks if you need to drain them later. Pour the water directly down the exposed pipes from the top drum. Continue filling the drum until it’s full and place a cap on top to seal it.
Pound a stake into the ground so that the top of the stake is level with the bottoms of the 45-degree bends. Tape a 1 in (2.5 cm) wide block to the end of a 4 ft (1.2 m) level. Place another stake about 3 7⁄8 ft (1.2 m) down the trench from the first one. Lay the end of the level without the block on the first stake and the block on the second. Repeat this process until you have stakes the length of the trench. Place gravel in the trench until the top of the gravel is level with the top of the stakes. Place 20 ft (6.1 m) of perforated drain pipe onto each hole on the second drum. Check the pipes with the level to see if the 1⁄4 in (0.64 cm) grade is consistent along the length of the pipe. Seal the 45-degree and 90-degree bends to the lower and upper drums, respectively. Fill the lower drum with water to prevent it from collapsing under the weight of the gravel. Lay landscape fabric over the gravel. Fill the remaining trench area with soil, compacting well to the original grade. Fill the upper drum with water.