There was another thread on this last year. One guy used clear PVC pipe for the bridge.
All the ones I have seen don't really have algae in them. Seen one set up for a few years and no algae. I would imagine leaving a fitting loose and cleaning that way if,you have to.Clear would seem to be nice so that one could see the fish and it not become just another hiding spot but I have some concerns. Can one make it in a way to clear the walls inside? I know that we never have algae problems but I do have to clean my filter tubes now and then? Maybe I would need to use regular PVC to avoid seeing inside??
Just some thoughts that I have not tried.