Hi Lizk, and Sandy, welcome to the portal. Are you asking about the drain line for a fresh water tank, or the drain for the sink?
From what i've seen with vikings, and it depends on the age of the pup and model, the fresh water tank, if mounted underneath the pup, has a spigot attached to it for draining. If the fresh water tank is under one of your dinette seats, inside the pup, there will be a spigot inside, against the wall of the pup with a hose through the floor for drainage.
For the sink drain, have a look in the cupboard under your swing up galley and see where the drain hose leads to. If it goes to the wall of the pup, that's where your drain is and they are usually either a garden hose hookup, or an approx 2 inch threaded hookup. If the drain line from the sink runs to the floor then crawl underneath the pup and you should be able to see a hose or spigot or drain of some kind there.
A lot of people will catch the grey water in a bucket or tub of some kind and dispose of it either in a campgrounds facilities, in the fire pit to douse the nightly burn, or dump it well away from the site, in the bushes or some such place.
Hope this helps.
BTW, throw your viking model and year in the signature line of your profile, or post what you've got and we'll be able to help you out a bit better.
Holey thread resurrection!
Good on you for searching previous topics on your issue carb1313 and welcome to the Portal!
Along the top of every page is a button for the owners manual's section here on P.U.P, here is the link for your Viking to down load and keep for your very own. http://www.popupportal.com/index.php?action=media;sa=item;in=2828
On page 18 it describes the grey water drainage, interesting though I see no reference to a shower option, only sink drain... simply tells to remove the drain cap and connect a garden hose. It does describe a P-trap so I would think there may be a low point drain fitting for winterizing.
If no one else chimes in with the answer, you may have to actually crawl under the P-up and check for yourself. They aren't that complicated and should be pretty clear on where it drains to.