It's a procedure used by vets to clear out the bowels before surgery and is highly effective. I do an epi-l on any beardie I acquire that has been kept on sand and have flushed significant sand quantities out of dragons who have never shown signs of impaction.
I only do this with assistance from a qualified vet, as there are risks to the procedure. First an anesthetic spray is administered to the back of the dragon's throat. Then an epigastric tube is placed so that it goes completely through the stomach and into the small intestine. This placement is critical! If the tube merely enters the stomach it can be hyperinflated to the point of rupture, which is why only a qualified vet should do this procedure.
Once the tube is properly placed, a mixture of pressurized gases, sterile saline and an enzymatic detergent are sent through the tube and the mixture is allowed to bubble up and loosen the gut contents for about an hour. Then a large quantity of sterile saline is sent down the tube to wash away the impaction. The effluent is saved, dehydrated and analyzed to determine the cause of the impaction.
This is the effluent I got from the gut of a 5 week old dragon who was kept on playsand since her hatching. About 1/3 of the vial contents are the playsand, the other 2/3 are bile salts, digestive juices, salt and enzymes from the detergent used to flush out the sand. It was 3.8 grams of material removed from a 5 week hatchling.
<img src="http://www.thebeardedlady.org/images/sand.jpg">
She was never acutely impacted, but in my experience almost all dragons kept on sand suffer chronic impactions. This is where sand grains slowly build up and coat the intestines, particularly the upper third of the small intestine where they are caught on the villi. Over time the dragon often loses the ability to absorb nutrients because of the sand clogging the villi and the dragon slowly starves over the course of years. Occasionally there is enough of a sand buildup in a pocket of intestines to compromise circulation and the tissue dies off. Acute sepsis sets in and the dragon dies within days or even hours. It's only when sepsis sets in that most people, even vets, detect a chronic impaction.
Most of the nearly 1,300 dragons I've seen who died of sand impactions were at least 5 years old and died as a result of chronic rather than acute impactions.