Clearing Heavy Blockage in the Main Drain

A stainless steel sink with water in it.

A major block may be caused by large items failing into the drains, or tree roots breaking into the drain system. Most main drain lines are four inches. The largest opening in the plumbing system is a toilet, and the trap on most toilets is only three inches. Anything that can get past the trap of a toilet most likely won’t cause a main line stoppage, unless there are roots or the line is broken.

There are a few tool options for this job.

Power Snake

For any of the major types of clogs in the main system a heavy duty sewer snake should be used. A hand operated snake will not clear a main line stoppage so an electrical powered snake is necessary. These items can be rented or purchased. This often is a job for a plumber. You do not want to damage the line running out of the house.

Drain Bladder

Home centers and plumbing supply houses sell a blow up ball that attaches to a hose and is inserted into the cleanout. When turned on, the bladder inflates sealing the drain and blowing high pressure water down the line This forces or pushes the stoppage into the main sewer line

It is important the ball be placed into the pipe, not just into the cleanout. Most cleanout are a Y-fitting with a 45-degree elbow. Push the ball into the cleanout at least a few feet in order to insure it is in the pipe.

TIP: Doityourself’s plumbing consultant Mark Vander Sande notes, “It is very important that this method is used on the cleanouts that are last on the drainage system. If they are used before, any water that is being used to “jet” the line will come out of floor drains, toilets, etc.”

There are several ways to access a major clog.

Basement Cleanout

Most older homes have cleanouts in the basement usually on the street side of the basement if you cannot remove the cleanout cap or plug you can break it out with a hammer as they are usually brass plugs. Once it is broken, you can usually unscrew it and buy a new plastic cap or plug at the local hardware store.

Exterior Cleanout

In most newer homes, there is an outside cleanout plug to access most of the system. Just locate the cap, unscrew the cover, and put the power snake through the system.

Roof Vent

Though the main drain can be accessed through the main roof vent for the entire system, this is the hardest to access and power tools can be a problem depending on the roof incline. This is not recommended for a do-it-yourselfer. Unless the roof is flat, it is very dangerous.

You are all set to clear out any blockage from your main drain. However, if you ever feel you are in over your head, don't be afraid to contact a professional.

Mark Vander Sande, professional plumber, contributed to this article.