How to Clean a Plastic Water Tank

Draining the Water Tank

Open the outlet valve or tap. The first step to cleaning your tank is to empty all of the water from it. To do so, open the outlet valve or tap at the bottom of your tank and let all of the water flow out. Connect a hose to the open valve in order to direct the water to a location where it will not cause any localized flooding or erosion. Permanent water tanks have a washout valve that is located at the base of the tank. If your water tank is permanent and contains a washout valve, use this to drain the tank instead of the regular outlet valve or tap.

Scoop water in the bottom of the tank out with a bucket. Since the outlet valve or tap is usually located above the bottom of the tank, you may need to remove some remaining water from the tank after draining it. To do so, use a bucket to scoop as much water out as possible. Once the water in the bottom is too shallow to scoop with a bucket, use a plastic cup or coffee mug to continue scooping it out.

Remove any remaining water. You probably won't be able to get all of the water out by scooping it up with a bucket or cup. Remove the remaining water using one of the following methods: Use a wet/dry vacuum to suck up any water that remains. If you have a small tank and can safely tip it up, you can do this to drain any remaining water from the tank. Once you've got all but a very small amount of water out of the tank, you can use towels to soak up any water that remains.

Cleaning the Inside of the Water Tank

Make a cleaning mixture. While you may be able to remove a lot of the sediment and residue from your tank without using a cleaning mixture, using one can help make this job easier. Simply mix hot water with laundry detergent powder or liquid to make a cleaning solution.

Scrub the inside of the tank. Use a bristle brush or abrasive sponge to scrub the inside of the tank, with or without your cleaning solution. Move your arm horizontally from side to side while applying a good amount of pressure on the brush or sponge. Continue doing this around the entire inside of the tank, until you remove as much slime and sludge as possible. You may need to use a brush with a long handle, depending on the size of your tank. This type of brush may be more difficult to maneuver, but will allow you to reach the bottom of the tank safely. If you're using a long-handled brush, you'll probably need to move the brush up and down vertically instead of horizontally. Avoid brushes with steel bristles or sponges made of steel. Plastic can scratch easily and these materials will probably be too harsh for a plastic tank.

Use a power washer. You can also use a power washer to clean the inside of your water tank. You can use the power washer by itself or in conjunction with scrubbing the inside of the tank, depending how tough the sediment and residue is to remove. Pressure washers come in a variety of sizes and strengths, but one with a pressure range between 1,300 and 2,400 psi works best for most household tasks. Follow these steps to clean the inside of your tank with a power washer: Fill your power washer with water or cleaning solution. Start by holding it about four feet away from the surface you're cleaning. Move closer until you find the distance that works best for removing dirt, sediment, and debris. Hold the pressure washer so the water hits the interior wall of the tank at a 45 degree angle. Continue this until you are satisfied that you've removed all the dirt and sludge from the walls of your tank. Pressure washers are very powerful, so always wear safety goggles when you're using them, never point them at another person or animal, and follow all other safety regulations. It is also a good idea to have someone with knowledge of power washers give you a lesson on starting and using them before using yours.

Use baking soda on particularly dirty walls. If you're having trouble getting all of the sediment and dirt off the interior walls of your tank, try sprinkling the walls with baking soda and scrubbing them with your brush or sponge.

Scrub corners and joints. While you are scrubbing, pay special attention to corners and joints in your tank. Residue stuck in these areas can be difficult to clean, so you may need to spend a little extra time getting into these areas. Try using a small toothbrush to help you reach and scrub these difficult places.

Rinse thoroughly. Once you're satisfied that you've scrubbed most or all of the residue from the inside of your tank, you need to rinse it very thoroughly. This is best done by using a hose to spray down the interior walls, making sure to get into all the nooks and corners. You can also use a pressure washer filled with clean water to do this. Alternatively, you can rinse the tank by filling it with hot water and letting it stand for several hours. Drain the tank, making sure you collect and safely dispose of the drained water. Repeat this process until the water is completely free of detergent and sediment.

Remove remaining liquid and residue with a vacuum. Some water tanks may not allow you to drain all of the liquid from them. For example, if your tank is too large to tip on its side and spray out, you probably won't be able to spray all of the detergent and residue out of the tank. In order to remove this residue, you can vacuum it out with the hose attachment of a wet/dry vacuum. Make sure you get the hose into the cracks, crevices, and corners of your tank in order to remove all of the residue. After vacuuming, you may need to take a clean rag or mop head and run it along the bottom of your tank to clean any areas that still have sediment on them.

Flush your tank's hoses and pipes. Pour some of your cleaning solution into these pipes and hoses. Then, use your water pump to pump the solution through the pipes, removing any sediment and dirt inside them. Complete the same process with hot water until the pipes and hoses are free of detergent.

Disinfecting the Water Tank

Fill your tank three quarters full with clean water. Once you've scrubbed out the inside of your tank, you can then perform the process of disinfecting it. To start, use a hose to fill your tank three quarters of the way full with clean water.

Add chlorine bleach to the tank. Next, add chlorine bleach to the tank in the ratio of 50 ppm (parts per million) to the amount of water. Follow these guidelines to determine how much household chlorine bleach (5% bleach) to use in your tank: For a 250 gallon tank, use 4 cups of bleach. For a 500 gallon tank, use ½ gallon of bleach. For a 750 gallon tank, use ¾ gallon of bleach. For a 1,000 gallon tank, use 1 gallon of bleach.

Fill the rest of the tank with water. After adding the appropriate amount of bleach, fill the tank to volume with clean water. This will allow the bleach to mix with the rest of the water in the tank.

Leave the mixture in the tank for 24 hours. Once you have the tank filled with chlorine and water, leave this solution sit inside the tank for 24 hours. Be sure no one comes in contact with the solution during this time because it can be harmful to people and animals.

Check the amount of chlorine in your solution periodically. During the 24 hour period that you are letting the solution sit inside your tank, use chlorine strips to periodically check the solution to see the amount of chlorine. You want to maintain a measurable chlorine reading throughout the entire 24 hour process. To check this, dip one end of the chlorine strip in the solution and follow the instructions on the packaging to determine how much chlorine is present. If there is no detectable amount of chlorine, repeat steps two through four.

Drain the tank completely. Using a hose, drain all of the solution out of your water tank. Hook the hose up to the valve on the bottom of your tank and allow all of the solution to flow out toward your sewage system. Make sure you point the hose away from any vegetation, lakes, and any other areas that may be damaged by the chlorine bleach in the mixture. Do not drain the tank directly into your water distribution system either. Remove any remaining liquid by scooping it out with a bucket and then using towels, a clean mop head, or a wet/dry vacuum to pick up the rest.