Wellllllllllllllllllllllllll, I think you may have misunderstood the Tostada, at least the way we use it. When rappelling, it is a Tostada, but when being pulled, it changes into a Taco. Otherwise there is no cleaning mechanism.
When looking at narrow slots, it is often best to set up the SandTrap many feet back from the edge. Partly, to give the trap time to clear before getting to the narrow spot. Partly, by the time it gets to the narrow spot the Trap might be flying through the air and go over the top.
Tom