This constant hitting your mouthpiece may damage the mouthpipe or other part of your instrument. Simply put the mouthpiece in the receiver and give it a slight twist to seat it properly. Check your valve springs, especially springs in the bottom of the valves, to see that their thrust is vertical and not sidewise. You can usually tell from the way the spring leans. Such a leaning spring exerts more pressure on the piston against one side of the casing than against the other, and tends to wear the casing out of round.
Some players use the second or third joints of their fingers.
This method pushes the piston against the opposite side of the casing, causing the piston to misalign slightly and produces bad valve action. Over time, this constant pushing against the opposite side will wear the valve casing out of round, creating valve leakage. It is almost certain, that a player who plays this way will have valve action trouble in the future. Screws have a tendency to loosen and back themselves out over a period of time. A little time spent checking over your instrument now, will save you a trip to the repair shop later.