All of the buildings that I maintain are heated with fuel oil that is stored in outdoor tanks. Outdoor storage tanks are prone to collecting water from condensation. Part of my fall maintenance plan is to check each tank for water.
Water is more dense than oil so it sinks to the bottom of the tank. To check for water in the tank I use a product called "Kolor Kut". It is a yellow/brown colored paste that comes in a tube. To use it you rub a little on the end of a dip stick and lower it into your tank. In this case I am using an old piece of pipe for a dip stick.
When Kolor Kut comes in contact with water it changes to a red color. In this photo you can see that the paste on the end of the pipe has changed to a pink color. There is about 1/2" of water in the bottom of the tank.
On many older tanks there is a drain on the bottom of the tank that can be used to remove the water, but newer tanks normally only have openings in the top. To get the water out of the bottom of this tank I used a Super Syphon. The Super Syphon is a handy little one way valve connected to a piece of clear plastic hose. It is a great way to transfer liquids from one container to another. They normally come with only 6' of hose but I put a longer piece on this one to use it on large tanks like this.
To make sure that I got the siphon all the way to the bottom of the tank I connected it to the dipstick with zip ties. This allows me to move the siphon around on the bottom of the tank to make sure that it is in the lowest spot. I have also used this technique to clean water or dirt out of the bottom of snowmobile gas tanks.