On my B36 the seacocks for the heads are 3/4 inch for the seawater inlet and, 1.5” (one and a half inches) for the outlet sea valve. As the toilets are the same size irrespective of which boat they are placed onboard, I can see no good reason to require different size sea valves. Also the wash basin outlet and the shower outlets are also each sized at 3/4 inch.