Yes, gray waste valves are 1-1/2". If you're replacing just the gate valves for your double waste valve then you can unbolt them and slip in the # T1003VP for the black and # T1001VP for the gray and then bolt them back in place. I've attached a video below where you can see how to do this.
If you end up needing to replace the entire double waste valve then shoot me a few pictures from the other side so I can see the direction of the piping to find the correct replacement. view full answer...
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