You have confirmed that the clog is 100% located in the standpipe (the vertical pipe in the wall that the sink and dishwasher share), and you have completely disconnected the dishwasher drain hose from that system.
Leave the plunger under the sink where it belongs—and never, ever let it near your dishwasher again. can you plunge a dishwasher
That pressure will find the weakest point—almost always the rubber seals. You might rupture the drain pump seal, crack the plastic housing of the sump (the basin where water collects), or blow out the gasket on the heating element. The result? The next time you run your dishwasher, you won’t just have standing water; you’ll have a pool of soapy water flooding your kitchen floor. Here is the most dangerous and disgusting risk. Your dishwasher drain hose is almost always connected directly to your kitchen sink’s drain pipe, often via a high-loop or an air gap (the little chrome cylinder on your sink deck). This is a direct plumbing link. You have confirmed that the clog is 100%