If they mix the contrast too thick you can get constipated. (Happened to me during the first one)
The best thing to do after you get home is to take 3 tblsp. of mineral oil in 4 oz. of water. It will help past it on easier. If you get no relief and feel like there's rocks inside you take another dose after 6 hours. Mineral oil is a very safe laxative, it's just greases the track.
It's no big deal to do the test. You stand on a special tilt table and drink the contrast. It's a little lemony, but very chalky. They then make you drink some fizzy stuff. It's to make your stomach swell up. You're told not to burp or you have to drink more.
They then tilt you back to laying down position. They have you lay certain ways and roll over and over. It's very hard not to burp during this.
Then your done.
Good luck on the test.