A few questions.
#1. Are the tiles removable, or glued down?
#2. How often do you clean up the poop?
#3. How often do you do clean the entire tank?
Poop should be cleaned as soon as you see it, with once a day being the minimum. If you are letting poop sit in the tank, bacteria, parasites, and viruses will be building up during this time, posing a risk for you and your dragons. Also, simply wiping the poop up isn't enough, you need to clean it. Many people use unsented baby wipes for the initial wipe down with good success, however you still need to disinfect the area. The strong poop smell is letting you know its time to clean, and that smell also means bacteria is building up. If you keep the cage clean, the smell goes away...this I can guarantee.
Assuming your dragons are healthy, you can use baby wipes to clean the poop up daily, then once a week clean and disinfect the tank. Once you get in a rythm, these weekly tank scrubs go quickly. You can use various products to accomplish this goal, but one product I really love is chlorhexidine, as it can be used to clean the tank and doesn't need to be rinsed away, and will not leave and toxic fumes behind.
I am assuming your tiles are not removable. If they are, simply remove the soiled tiles and clean them in the sink using warm soapy water. You can then bake in an oven at 320 degrees for 1 hour, or you can soak in a disinfectant solution. If your not in the mood to hand scrub, simply put them in the dishwasher on the potscrubber setting.
For tiles glued in the tank, do the following.
Step 1 - Remove the dragons from the tank
Step 2 - Remove all cage furniture, such as rocks, leaves, logs, etc.
Step 3 - With a scrub brush or sponge, scour tank with warm soapy water, and rinse when finished. Make sure to clean all soiled areas until all fecal matter and soil is removed.
Step 4 - Using your disinfectant of choice (properly diluted), thoroughly wet the entire tank with the solution, and let stand for 30 minutes. A 10% bleach solution is a great odor remover! After the soak time, rinse the tank until there are no fumes (if using chlorhexidine, simply wipe up the excess with a dry cloth).
Step 5 - Clean all tank furniture with warm soapy water, then soak in the disinfectant solution for 30 minutes. Rinse well once complete. Alternatively, stone/ceramic and wood items can be baked in an oven instead of the disinfectant soak. For wood, use 275 degrees for 1hr, for stone/ceramic use 320 degrees for 1hr, taking care not to cool the items too rapidly at the end (may cause them to crack).
Step 6 - Replace all items back into the clean fresh smelling tank.
You do the above, and your tank won't smell anymore...this I promise. Also, to answer your other question, sand will not hide the odor. In fact, sand will harbor smells and be harder to clean...the tiles you are using are the best substrate for beardies.