it is 3 inches all the way across including the washer. so i would guess 1.5-2 inch.
i have it ghetto rigged so that the leaking water funnels back into the sump.
i will just get some bulkheads tomorrow.
I'm positive I have one of these and I just tore my whole closet apart looking for it. No luck! Sorry i couldn't help...I live right by you (Marshfield & Cortez)