An analogy made by the pastor at church on Sunday.

Say you fill a glass with water, all the way to the very top and set it on the porch on a summer day, you make sure everyone knows to be careful and not knock it over.
A few months later you come outside to look at the glass, it will most likely be much emptier if not entirely. It will probably be dirty and you will doubtfully want to drink from it.

We should be continually filled with the Holy Spirit, not just one time but continually every day overflowing. Like the glass, filling up once and then thinking we're done won't really work.
And sometimes we'll leak, we'll probably leak a little every day but all we have to do is ask our Lord to fill us up again, overflowing.