I am installing a washing machine and hooking into what was a shower drain.
There will be no sink. I want to add a check valve to prevent dirty water flowing back into the washer in case of a clog.

What type of check valve am I looking for?

I haven't been able to find a suitable one at the local Home Depot.
I am hooking into a standard shower trap, I believe it is 1 1/2 inch ABS.

Thanks...

For this installation you won't need a check valve. Simply convert your shower trap into a washer trap and stand pipe. This will give you a regular standard washer drain hookup. Just prime and glue a 1 1/2" coupling, (I'd much rather it be 2") on the shower stup up and a piece of ABS pipe on the coupling 2" higher the rim of your washer. You may then hook the washer hose into the stand pipe and proceed to wash away.
To answer your question, if your setup needed a check valve, (which it don't) then you would need a spring loaded hose check valve. Regards, Tom

Thanks much speedball!