Yeah definitely not a good idea and it will siphon the trap like John said. Also like John said you can't double trap. There's a couple ways you can re do it properly. I feel the best way is to on the vertical piece for the washer put in a sanitary tee, on the top of tee connect a vent, best way is if you have a vent already that you can tie into, or you could do an AAV for a vent. Then off of the side outlet you put in piece of pipe that is minimum 2x diameter of pipe ex. If pipe is 1 1/2 you need a 3 inch long piece between trap and tee. Then you need a 24" piece coming up vertically on the other end of the trap. The top of that 24" piece must be 36" off the floor, if its not then make the 24" piece longer. These are all minimums I have stated. And off the top of the tee, your vent must be tied in above flood level rim of the washer, so if the drain backs up then the vent doesn't act as a secondary drain. And I'd suggest a cleanout, I'd install it in the vertical portion either above or below the sanitary tee, I'd put it in the vent portion, and lastly be sure to use a union trap. Technically speaking laundry needs to be 2" drain according to code. These codes are all based in Canada FYI in alberta specifically, so they all should apply to you. Best of luck if you have any questions let us know!
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