The drip rate is controlled by the correct drip emitter. For small tanks, like 15 & 20 gallons, they will get 1 gph (gallon per hour) emitters, 29 gallons get 2 gph, & 55 gallons get 3.3 gph emitters or a couple 2 gph's. I used pressure compensating emitters, because they are agricultural grade, and claim to be the best on the market.
On my drilled tanks I use bulkheads/standpipes and on my non-drilled tanks I use a siphon overflow device.
The overflow device is effective, yet cheap to make. ($4- $5 each) Think of this device as a hang on power filter like an aquaclear 300. If the aquaclear pump stops working, water will remain in the filter box from the intake tube siphon. The water line equalizes between the two.
Now, picture this.... The overflow device "is the aquaclear filter box" the black elbow at the top determines the water level. The green hose attached to the black elbow goes into another 1½" PVC drain pipe which is gravity fed into a big vat outside of the fish room.