Dear customer, DHU800 (with drainage pipe) is a classic model with 800ml water tank and about 200ml/D dehumidification under 80% humidity, DHU1000 is newer model with ½ size of DHU800 but the water tank is 1000ml, and DHU1000 is 300ml/D dehumidification under 80% humidity. However, please note that DHU1000 cannot use drainage pipes due to its compact design. Thanks!