What is meant by the "diaper" whose presence, when a transparent fluid is discharged, does not nullify ablution?

It has not been said that transparent fluid does not invalidate ablution; rather, it does. However, if it continues for an uninterrupted period, it takes the ruling of perpetual discharge (sals), in which case its owner performs ablution for prayer after the time for it has begun, and prays with it one obligatory prayer along with as many supererogatory prayers as possible. As for the diaper, it is what prevents the discharge from spreading.