Aside from the sand the question seems to be how to get the multi-port off. What kind of a valve is it? Make / Model if you have it. Sounds like a top mount valve and they are usually held onto the tank with a clamp band. Take the band off and the valve assembly should come right out maybe with a little wiggling and twisting. That also assumes the thing isn't hard plumbed into the system so you would have to cut pipes to remove it. Let us know. As for the laterals, you should fill the tank with water somewhat above the laterals before adding sand. Cushions them from the dry sand and will prevent damage when refilling.
Al