I didn't use any of the formal vacuum bag fittings. I ran a 1/2" white pvc pipe from the pump to the bag, wrapping the bag around the end of the pipe.
I perforated the end of the pipe to ensure that it wouldn't inadvertently get clogged, and I added a fitting for a pressure gauge and a water trap near the pump itself.
The water trap didn't have a lot to do with the vacuum bagging operation. I had a leak in the hull of a boat I then owned and needed to get water out of the foam core of the composite hull. The pump was rated for continuous duty, so I set it up for this and left it on for a week. Dried the hull out and then I repaired the leak itself.
It was well after that that I started using it for vacuum bagging. Still, I feel that the trap does give a small bit of protection to the pump.
Dave