I have done several other posts about the Johnson Tee and their use as an alternative to the countertop style air gap device for dishwashers.
While I like these devices quite a lot, because they eliminate the need for having a device installed on the sink or countertop, it has come to my attention that some modern dishwashers require a 5/8” drain line from the washer. In order to make these dishwashers quieter they use less noisy motors that do not have the pumping capacity of older noisier motors. The larger size drain minimizes clogging that might result with smaller diameter drains.
There are still lots of dishwashers—even really quiet ones—that still allow the ½” drains typical of Johnson Tee’s. The problem might arise if one has a Johnson Tee installed and one buys a washer that requires a 5/8” drain line. This is not a big issue as the Johnson Tee would need to be properly abandoned and a countertop style air gap device installed. The other option of course would be to find a washer that allows for a ½” drain line.
Some of the dishwashers that I found installation instructions for that require a minimum 5/8” drain lines were GE, ASKO and Bosch—there are likely others.
Some of the dishwashers that I found installation instructions for that require a minimum 1/2” drain lines were Whirlpool, Kitchenaid and Amana—there are likely others.
There also may be different “models” of many of the manufacturers’ that either allow or don’t allow a ½” drain line.
Some jurisdictions do not even require air gap devices—or are not enforcing codes that do require them.
Every dishwasher installation’s requirements must be met regardless, and this is why installation of a dishwasher should only be done by a qualified professional.
By Charles Buell, Real Estate Inspections in Seattle
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