'people' have said that you don't want to use too much rigid PVC glued together as the result is a rigid but brittle structure, and it will eventually crack under repeated movement on a boat. I think that could be true, but if the pieces were fairly short and made flexible with hose at both ends, it should last a very long time. Next, there is no way you will get good quality waste hose over the 1 1/4 pipe. It is 1.66" OD, a pretty big mismatch. But you could find some 1 1/2 hose adapters and make it work. Sealand used to make some for this purpose. All of the fittings required may use up more space than you have. It is very easy to take a short piece of pipe and turn it to make an adapter.