*PLUMBERSSTOCK EXPERT* responded:
Hi! Thank you for your inquiry in our Norwesco 62397 20"D X 15"H manhole extension. First, you need to take the lid off the tank and install the manhole extension on the tank. Then, the lid goes on the top of the extension. If you wish to have access to our exclusive discounts and limited offers, you can sign up for our newsletter by entering your email address in the area provided on the lowermost part of this page. Have a great day!