Using the density, find the volume required per minute.
From the volume required per minute, divide by the cross-sectional area of the cylinder to get the decrease in height per minute.
This decrease occurs in 1 minutes.
In 1 day, there are 24 hours, 24*60 minuntes.
In 3 days, there are 24*60*3 minutes.
Find the total change in height now, using the time and rate of decrease in time.