Keep in mind that 1-1/2 PVC has an ID (inside diameter) of slightly greater than that dimension (it's ID is 1.59"), and OD (outside diameter) of 1.90".

Vacuum hose diameters vary quite a bit. Your best bet is to go to your local hardware and try different PVC couplings with a sample of your PVC and vacuum hose. You might have to use 2 couplings.