A kitchen sink full of water that won't drain is an annoying but fairly easy problem to solve. The blockage might be due to a build-up of grease or waste that has washed down the drain, or something that has fallen down the drain and blocked the pipe. You have two access points -- one is the plug hole, the other is the U-shaped trap under the sink. Finding the blockage is a process of elimination.
Leave the water in the sink for now, as the weight of the water helps to push the blockage downward if you locate the problem. If the water is uncomfortably hot, wear rubber gloves or add some cold water.
Place one hand over the overflow hole in the sink, or use a damp cloth. This prevents air escaping during the process and maintains pressure when using suction. Place your other hand palm downward over the plug hole and push firmly against it, and then remove your hand quickly. This creates a suction effect and might loosen the blockage. If not, repeat the process five or six times.
Use stronger suction by using a sink plunger. Cover the overflow hole again with one hand, or a damp cloth, and place the cup of the sink plunger directly over the plug hole. Push down firmly to create suction, which you can feel by moving the plunger slightly. Good suction will mean that the plunger cup doesn't move.
Pump the plunger over the plug hole and then pull it up firmly away from the plug hole. If the water still doesn't drain, repeat the process with the plunger five or six times. If this doesn't work, investigate further down the waste pipe.
Remove as much water out of the sink as possible, using a small saucepan or a jug. Place a bucket underneath the trap of the U-shaped waste pipe under the sink to catch water when the trap is opened. Unscrew the collar, using a wrench if it is tight, and allow water from the trap to drain into the bucket.
Check if the sink has drained of any remaining water. If not, insert a plastic-covered wire to check for blockages on either side of the trap. Remove the waste if possible, or dislodge it and turn on the faucet to flush it out of the pipe into the bucket. Do not flush the waste down the lavatory as it might cause a blockage further down the waste pipe -- instead, wrap in paper and discard in the trash.
Fit the trap together again, ensuring that the rubber seal is tight and that you replace it in the original position. Leave the bucket underneath the trap to catch any leaks once you have unblocked the sink, as you might need to reposition the seal. If this process hasn't worked, try a chemical drain unblocker or a combination of bicarbonate of soda and vinegar. Note that the latter option should not be used on plastic pipes as the heat generated will melt the plastic.
Read the instructions on the chemical drain unblocker, making sure to wear eye protection and gloves. Open a window to allow air to circulate if the room is not well ventilated.
Remove small children, animals or fishtanks from the room, and cover food or put it away. Pour the recommended amount of cleaner into the plughole, and follow the instructions for the length of time to leave it to work. Leave the room to avoid inhaling fumes, and shut the door.
Wait for the recommended length of time and follow the instructions on the container about rinsing the product away -- some chemical cleaners require a second application, while others advise that you flush the waste pipe with boiling water. If this is unsuccessful, investigate the outside waste water pipes.
Check your house plans to locate the inspection chambers along your external drainage system, and open the first one. The lid is probably very heavy so ask someone to help you lift it. If the chamber is empty, the blockage is somewhere between the house and the chamber, whereas if it is full, the blockage is somewhere in the pipes leading to the main drain.
Tackle the waste pipe with drain rods. Wear eye protection and rubber gloves. Insert a plunger rod into the pipe leading to the house, and screw on another rod to push it further in. Continue adding drain rods, turning them clockwise to ease the transit through the pipe. If the rod reaches an obstruction and it won't shift, remove the rods one by one and replace the plunger head with the corkscrew rod.
Repeat the rod insertion through the pipe until you reach the obstruction. Continue turning the rods so that the corkscrew embeds in the obstruction. Withdraw the rods and dispose of the solid waste.
Fill the kitchen sink with hot water and pull out the plug. This flushes the pipe through to the inspection chamber. Keep the tap running until the water emerging at the inspection chamber is clean. Finally, pour boiling water down the plug hole to dislodge any grease or debris that wasn't flushed out by the hot water.
Check the remaining inspection chambers in sequence if the blockage is further down the line to see if one of them is empty, If so, perform the same procedure on the inlet pipe to the inspection chamber until you clear the pipe. The blockage might be in the main drain, in which case the relevant local water authority needs to investigate.
Contact a plumber if you are not able to unblock the system yourself. Call two or three plumbers, describe what measures you have taken so far to find the blockage and ask for quotes. Word of mouth is a good advertisement and you might know someone who can recommend a good plumber.
Check that the plumbers are state licensed and that their licenses are up to date. Reputable firms will be pleased to confirm their status.
Arrange a date and time for a visit. When the plumber arrives, explain again what you have done so far, what chemicals you have used, and how far along the waste water system you have investigated to find the blockage.
Keep waste pipes clean and fresh by pouring boiling water down after washing up to loosen and flush away any grease or waste. Once a week, pour a cup of washing soda into the plughole and leave for 15 minutes, before washing it away with boiling water. Use a drain guard or filter placed over the plug hole to catch all the waste and to prevent it blocking the drain. Some chemical drain unblockers can be poured through standing water and will sink down into the waste pipe to dissolve the blockage. Check the manufacturer's advice on the container. Plastic-covered wire is often used for hanging net or light fabrics, and is flexible enough to be a useful tool for exploring the pipework for blockages.
Chemical drain unblockers are toxic to aquatic wildlife. Lee Hickman, in his article "How Should I ... Unblock a Drain" in Guardian Online of Jan. 3, 2006, quotes the European Chemicals Bureau's findings and suggests alternative drain unblockers that do not pollute water or harm organisms. Remind everyone not to use the kitchen sink faucets, or taps, until you have finished working on the waste water trap and have replaced the cap.