I'm pretty sure that it's Robotussin Maximum Strength. You're going to want to drink about 6 oz. (one four-ounce bottle and half of another works well.) Of course, you can go to your local store and see if they have Dex-Alone, an excellent product where the only active ingredient is DXM. It's very, very safe, and it's what I use. Also, you can go to www.dextroverse.org and check out the extraction method to use with sucrets, it works rather well too. You might want to take a general look around that site as well, it has great information on using DXM in general, warnings, tips, etc.

Good luck, let us know how it goes!