D0 - The Y position on the screen the water will drop from. If set to 0 will default to -16.
D1 - Amount of frames before the initial drip. If set to 0 will default to 20.
D2 - Amount of frames before another drip. If set to 0 will defualt to 160.
D3 - Max amount of random frames added to the D2 delay.
D4 - Sprite ID to use for the ripple when landing. If set to 0 will default to 137 (for personal reasons deal with it :) )
D5 - ID of SFX to play when drip lands.
D6 - Velocity of water drop. If set to 0 will default to 2.

Place an FFC on the screen with the graphic of your drip in the location it should drip to and assign this script and the variables.
Set the flag "Run Script at Screen Init" to avoid the drip being visible on-screen before it falls. Also recommended to set the "Draw Over" flag.