Each reservoir comes with a specially designed lid containing an access port and a raised grip porthole cover.This standard option allows the gardener easy access to the reser voir without taking the entire lid off, ensuring a more functional routine when adding solutions, nutrients and water to your reservoir. The MULTI-RES Reservoir also comes equipped with built-in bulkhead ports in front and on each side, enabling the grower to add a centrifugal pump outside the reservoir.This feature also gives the gardener the ability to join reservoirs together in-line or side by side to achieve increased water volumes.