i use a 3" pvc thin wall coupler, it had a ridge in the middle which i used a hacksaw to cut it in the middle. Then i used that flanged area next to the subaru maf piece which i cut out of the stock subaru air box. I used long pieces which i used plyers to break off the subaru air box and put a match to it and let it burn and as it was burning i would work it in the joint and the little fire will melt both plastics together and also melt the plastic your using at the same time. I also did the outside as well. when done you can't break these two pieces apart.