I've never had this as an issue - but do the job the way Cleversod describes.
Putting silicone sealant in takes a bit of practice, though not rocket-science to get a decent finish.
if you follow cleversod and grout twixt tile and w'top then,,,, wait for it , apply a very thin bead of clear silicone you will be amazed you can hardly see it hth Tez