If you're using poppy seeds, it shouldn't taste too horrible on it's own. If it came out milky and/or smells a little funny you probably let the seeds sit in the water too long. It's no good if they sit because not only do the seeds start to release a bunch of digusting fats and oils after a bit, they also start to absorb the water (with all those good alkaloids in it.)
You want to 'wash' the seeds as opposed to making a tea out of them. Don't let it 'steep' or anything like that. If you use lemon juice with the seeds, make sure to only use a little bit. Too much is a bad thing and can make the tea difficult to drink.
Once you've put the seeds and water (enough to cover the seeds) in the bottle you should shake it as vigorously as possible for about 3 minutes max, then drain the liquid and drink it. The seeds are good for a second wash if you do it quickly, , although it is less potent than the first. I personally wash the seeds twice back to back, combine the first two washes into the same glass and drink it like that.
Sugar can make it pretty palatable if you're having trouble drinking it at first. It does take some practice to get the method down pat, but remember that you're washing the goodies off of the seeds, not extracting them, and you should be alright.
The seed tea also has practically zero shelf life. The clock to it spoiling starts pretty much as soon as water touches the seeds, so don't try to store it or save it for later...it won't be any good.