Unless the bucket is smaller at the top than the bottom (and most are the other way--wider at the top), it's likely to lose water faster than the pool. 5 gallon paint buckets are straight-sided so their rate of loss is the same, given what Mark pointed out.
1/4" per day is a lot (assuming that's 1/4" more than the bucket), and if it's still doing it with plugs, you have a leak in either the pool wall or around the fittings. I can think of a number of causes of leaks when the returns and drains are uncapped. I wondering about a badly cracked return/drain fitting, that seals partially with a plug...But that's idle speculation.