[EDIT]. It depends on the design of the autofill.
The auto fill is [EDIT] fed by a water source, hose, sprinkler line, etc... plumbed to a float similar to a toilet float with a pipe from there to the pool.
[EDIT TO ADD]. Some designs do have a drain built into them. Others don't.
The only way for water to drain (other than leaking) is manually, using a pump, or by a built in overflow.
Most pools have a built in overflow but not all. Its just a pipe installed at what the water level should be when the pool is full. If the water level gets too high from rain, or from the autofill, water will drain out the overflow.
The overflow can look like one of 3 things.
1. A retun fitting without the eyeball that really isnt a return.
2. The overflow may look like a skimmer mouth on a gunite pool with a pipe routed to the street curb, or part of the yard or almost anywhere I guess that the PB routed it to.
3. An overflow pipe built into the autofill. It will be visible if you remove the top and look in.
It may well be the float was set too high, which would indeed result in a small constant draing of water via the overflow. If this is the case, then teh autofill will probably also be always
on and providing a continuous flow of fill water to the pool. This might result in a higher than normal water bill too.
Easy leak test to ease your mind.
Fill a 5 gallon bucket about 3/4 full of water
Use a sharpie and on the INSIDE of the bucket, put a mark at the water level.
Now sit the bucket on the steps of the pool.
Use the sharpie and put a mark on the OUTSIDE of the bucket at the pool water level.
Monitor it for a few days.
If the water level on the outside of the bucket drops more than teh water level on the inside of the bucket, then you have a leak in the pool.
If there is no discrenable difference in either of the water levels, then its not leaking.
