Just as was said before I have had 3 Keystone Montana's and I would think Alpine would be the same the drain pex tube is hanging underneath behind the rear axle with a white cap on it ,in the future it might help ya if ya joined the Keystone owners Forum http://www.keystoneforums.com/forums/index.php and they would tell ya EXACTLY where it is,The Montana owners forum has helped me A lot and I think the folks at the Keystone Forum would know just about anything about your Alpine
2015 Montana 3735MK Legacy,2007 3500HD GMC Dually LBZ Duramax/Allison ,Pacbrake,Firestone Airbags Bullydog Tuner