Reuben's Home Inspection Blog


Missing Cleanout Plug? It Might Be An Expensive Repair.

One of the most common defects that I find in old Minneapolis and Saint Paul houses is missing cleanout plugs in floor drains - especially during Truth In Sale of Housing Evaluations.  Missing cleanout plugs can allow hazardous sewer gas in to the home, and often indicate a clogged floor drain.   To learn why and how, read on.

Trap Diagram Every plumbing fixture has a trap.  The purpose of a trap is to prevent foul-smelling sewer gas from coming back in to the house.  The diagram at right shows a P-trap, which can be found at sinks, showers, and bath tubs.   The left side of the trap connects to the plumbing fixture, and the right side connects to the sewer.  The 'sewer' side will have sewer gases present, but the water sitting in the bottom of the trap prevents the sewer gases from entering in to the house.

Floor Drain with water Floor drains are no exception.  The photo at right shows a floor drain, as viewed from the side.  The shaded portion shows the trap where water will always sit, which prevents sewer gas from coming in.  When you look at an installed floor drain, all that you typically see is the grill on top; the rest of the drain is always buried in the basement floor. 

When the drain line gets clogged  If the drain line for the floor drain gets clogged, it needs to be cleaned out with a drain cleaning tool. The floor drain has an area which bypasses the trap, which will allow a tool to be inserted in to the drain.  I've highlighted this bypass in the photo below, left.   Normally, a plug is always in place here, because this is an area where sewer gases dwell.  When the plug is removed, sewer gases come in to the house.  After the drain gets cleaned out, the cleanout plug needs to be replaced.   The plug is circled in blue in the photo below, right.

Floor Drain bypass Floor Drain showing cleanout plug

Bad Threads on cleanout hole What if the threads are destroyed?  On some older floor drains, the threads that used to accept the cleanout plug are damaged or badly rusted, to the point that it's impossible to screw in the cleanout plug.  The only acceptable repair for this situation is to install a rubber plug that is sandwiched with two pieces of metal that expand the rubber when tightened together.  The two photos below show a rubber plug before it's tightened and after it's tightened. 

 Loose Cleanout Plug Tight Cleanout Plug

A missing cleanout plug usually means one of two things:

  1. The drain was clogged, someone removed the cleanout plug to clean the drain, and they forgot to put the plug back in.
  2. The bottom of the trap is clogged, and someone removed the cleanout plug to allow water to drain directly in to the sewer, instead of going through the trap.

Any time I see a missing cleanout plug, I tell my client that the cleanout plug needs to be replaced, and the floor drain may need to be cleaned out or replaced.  If the drain cannot be cleaned, the entire floor drain needs to be replaced.  When I perform re-inspections on homes in Minneapolis that have had missing cleanout plugs, about one in five floor drains need to be replaced because the drain couldn't be cleaned out.  This is an expensive repair, as it involves breaking up the concrete in the basement floor, replacing the drain, then pouring new concrete.   

Just for fun, here are a few photos of missing cleanout plugs that I've taken within the past couple months.

Missing Cleanout Plugs

Reuben Saltzman, Structure Tech Home Inspections - Email - Minnesota Home Inspections

Reuben Saltzman, Structure Tech Home Inspections


Comment balloon 13 commentsReuben Saltzman • July 28 2009 06:25AM


Great information

may be more than I ever wanted to know!

your friend in Charlottesville Virginia!

Posted by Charles McDonald, REALTOR®, Blogger, Principal Broker®, Owner (Charlottesville Real Estate Solutions) almost 11 years ago

Fantastic post Reuben.  Great pics and explanations.  I may have to link to this one in my reports.

Posted by Jim Allhiser, Salem, Oregon Home Inspector (Perfection Inspection, Inc.) almost 11 years ago

Charles - good!  Better than too little.

Jim - Thanks, I wrote this for exactly thet reason.   I just found another missing cleanout plug at my morning inspection, and I linked to this post in my report.

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) almost 11 years ago

Reuben, I don't see many floor drains here in CT. Some are nothing more than a hole left open in the slab and covered over with boards. Great information and well written.

Posted by James Quarello, Connecticut Home Inspector (JRV Home Inspection Services, LLC) almost 11 years ago

James - it sounds like there's a lot less that could go wrong with your version of a floor drain!  

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) almost 11 years ago

Very good stuff here.  Thanks for the education.

Posted by Joshua Frederick, Home Inspector in Defiance & all of Northwest Ohio (Home Inspector for ASPEC Residential Services, LLC) almost 11 years ago

My doctor's office has one missing on the outside of his office.  I've told him about stuff dropping in there and causing a more expesnive resolution to get his sewer cleaned out.  Mentioned it twice this summer.  Sooner or later something's gonna drop in there and clog his lines.

Then he'll be PO'd that it cost so much to get it cleaned out.  Ah well.

Posted by Erby Crofutt, The Central Kentucky Home Inspector, Lexington KY (B4 U Close Home Inspections&Radon Testing ( almost 11 years ago

We don't have too many floor drains out here. Even when they put the kitchen and laundry room upstairs, they conveniently skip putting a floor drain anywhere near the washer and dishwasher.

Posted by Not a real person almost 11 years ago

Russel - yeah, I suppose without a basement, why bother?

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) almost 11 years ago

Where can I get one of the expanding rubber plug? I don't see them in the hardware/home improvement stores...

Posted by Wendy over 9 years ago

Hi Wendy, check out

Posted by Reuben Saltzman, Delivering the Unbiased Truth. (Structure Tech Home Inspections) over 9 years ago
Finally some nice pics with an explanation. I need more info on how to get the drain cover off.
Posted by sarah over 6 years ago

Hi Reuben, My parents have a floor drain that has water standing in the drain, the clean out plug is missing. I went outside and looked in their septic clean out pipe and there is water standing in it about a foot down the pipe. My parents are elderly so I am trying to find out the best way to get this fixed for them. There is no sewage backed up in the house (in the sinks, toilets, showers, etc) My Dad said it has been like that for a while and he thinks the clean out plug fell down into the floor drain. Any suggestions please? Thank you, Amanda

Posted by Amanda Marshall 5 months ago