The check valve is not 100% necessary and many just do away with it (it was also only on the later cars). It was said the function of the check valve was to prevent a little oil smoke from the exhaust at full boost and prevent high pressurization in the vent line (like if the line gets clogged with oil accumulation). I have not noticed a difference with or without it since i removed it. You can replace that hose with just a 3/4'' or 19mm silicone or rubber hose(make sure its oil rated...IE; not radiator hose).
Look up the 'venturi delete thread' on Rennlist in the 951 forum. There is a good thread that shows one way of plumbing everything if you wish to retain the check valve. Personally i think its more trouble than its worth.
This was my solution using a 19mm 90* elbow and some 19mm straight hose. I deleted all the hardpipes under the intake to simplify the routing (i had already deleted the CV, so i didnt need any of it). You can essentially do the same. This picture shows how i had this setup when i was still running the stock turbo and no catch can. I had one 90* elbow, some 19mm silicone hose and a 45* 19mm elbow to attach back to the stock j-boot. I also had a few 19mm couplers to connect everything. You can basically do the same and retain all those hardlines, you would just need a 19mm 90* elbow.
This is what the original hose looked like when i pulled it with about 100k miles.
