Seller’s confused about plumbing jargon
DEAR BARRY: The people who are buying our home hired a home inspector. He said that our dishwasher drain hose needs an airgap to prevent a sewage backup into the dishwasher. Unfortunately, there is no place to install an airgap because the hole on the back rim of the sink is being used for the water purifier.
Instead of an airgap, our handyman has installed a check valve, but the home inspector says this does not comply with code. The handyman says that airgaps and check valves are equally effective and that even a high-loop drain line can be used to prevent back-siphonage.
Again, the home inspector disagrees. To us, this is all a bunch of confusing terminology. Meanwhile, the people who are buying our home insist that the problem be corrected in an approved manner. How do we sort through all of this conflicting technical jargon?
— Kathy
DEAR KATHY: Your question covers a number of issues and misconceptions regarding dishwasher drain lines. Let’s take them one at a time:
• Most people have seen a dishwasher airgap. It appears as a small chrome cylinder, commonly found on the back rim of a kitchen sink. It is what plumbers call an anti-backflow device, because it prevents sewage from flowing back into the dishwasher.
Your buyers’ home inspector was correct in recommending that an airgap be installed. Alternative devices are available, but airgaps are specified in the plumbing code because they are the most reliable in all circumstances. It should be noted, however, that airgaps are not required in all states. Therefore, your local building department should be consulted to determine the requirement in your area.
• A check valve is also an anti-backflow device and also will prevent sewage from siphoning into your dishwasher. The problem with a check valve is that it is not foolproof. If a piece of food gets caught in a check valve, the valve can be permanently stuck in the open position, thereby defeating its function as a health safety device. This is why an airgap is preferable.
• Many handymen and older plumbers use what is called the high loop method of installing a dishwasher drain hose. This method can be effective in preventing back-siphonage, but only with low pressure, low level sewage backups. When a sewage backup is under pressure, or when a backup reaches the level of the sink rim, the high loop method is ineffective and will allow raw sewage to flow into the dishwasher and onto your dishes and tableware.
If your sink lacks an available hole for installing an airgap, a plumber can usually drill an additional opening. Another way to provide a hole is to replace the standard type sink faucet with a post-type faucet, one that does not have the rectangular mounting plate at its base. Without the mounting plate, two holes will be exposed in the rim of the sink. One of these can be used for an airgap. The other can be used to install a soap dispenser or a handsprayer.