I agree, do NOT take possession of it and do not claim it, and deny any knowledge of it, but it sounds like you are already past that by admitting enough that they returned the tube to you. And why the fuck would they return the tube and not the contents? I would say you have a right to be worried still at this point. I sent a seed package a while back that made it just fine with a treasure trove of good genetics in it that I fretted about for three days as the last THREE packages I sent containing other illicit things did not make it, and it was very discreetly packaged. I never put a correct return addy and always use the same false name and addy when I mail something that I know is a actual place.
I used to have a friend who was a postmaster in a small town. He gave me a few pointers for illegal mailing.
#1 first and foremost, DO NOT use some witty fake name and address and make sure it is an actual address. As soon as it is scanned and a name like Smokey Toohigh at 420 assmaster lane the package is flagged suspicious. Always use a realistic name and an actual return address. (Not your own) that will not flag the package as soon as it is entered into the system. Always use a return addy and never leave it blank or it is flagged for that also.
Do not use too much postage like putting 6-8 postage stamps on a bubblemailer and dropping it into an anonymous mailbox.
Do not use Duct tape to reinforce your packaging. Overpackaging is suspect.
Do not use overnight mail or UPS or FED EX as every single package they handle is Xrayed and looked at. Always use regular parcel post and even then it is getting to the point that most of those packages are scanned as well as the USPS is increasing their automation and security with homeland security funding.
Always make sure there is no smell, I have gotten packages at the post office I could smell ten feet away from my goddamn po box! That is the least you can do for your and your friends security! If you send pot use a glass jar with a well sealing lid and well protected from breakage with several inches of bubblewrap around it.
Usually if a package gets busted open, they tape it up and send it along even if they see small amounts of weed or illicit drugs. Depending on the actual person involved of course, but the postal inspectors and feds have better things to do than run down everyone sending their cousin a couple grams of stinky greenbuds.
Good luck on your situation Saph, and my instincts tell me this is going to coxme out ok or you would have already had a visit. Let them send it to your parents, maybe they will even be cool and give it to you if they get it.