Hello;

My Dishwasher has been running fine for years. About three months ago I noticed water in the bottom of the basin and it smelled rotton.

Here's what's happening:

The dishwasher runs fine and drains fine. When I wash dishes in the sink and drain the sink water, the water is dumping back into the dishwasher. Is there a check valve that needs to be replaced? What would cause this? The drain hose, from the dishwasher is elevated and no change to this hose has taken place. It does drain into the disposer.

Any advice would be appreciated.

Thank You,
NickyD.

You asked if Whirlpool built into that drain system a reverse-flow-prevention check valve. That is good thinking on your part and good design by dishwasher manufacturers, since sink and garbage disposal drain water flowing down into dishwasher sumps would, could and, apparently in your dishwasher's case, can create a biological hazard for your family dining with those washed forks, cups etc.

Yes, there is a check valve in that drain system. Somehow yours is not preventing back flows. Immediately pull it out and restore it to proper back-flow sealing operation. Typically, that only requires cleaning rather than replacement.

I'm not one who immediately assumes that all defects are to be expected. But some of the stringy clumpy trash dishwasher pumping systems are forced to handle are sometimes able to hang together and block check valve action. I don't know how manufactures could prevent that for any reasonable manufacturing cost.

It's good that you were sufficiently observat to know that this problem exists. This is one problem which should NOT be ignored and tolerated.

Access will require pulling out the dishwasher. The check valve is after the drain pump but before the drain line going up to the sink or dishwasher connection.
Good Luck,
John