Screening sunken gas tank

My front garden gets the best light. I want to make much more of it. It has a partially sunken gas tank that has been covered with grass but there is still a ‘telly tubby’ grass mound that takes up a third of the garden. How can I screen this. I still need to have access to the tank for gas re-fills.
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We need far more information and a photo or 2.
Can't recommend plants if we don't know how much sun you get, how big the area is, sort of soil, clay, chalk, sand?
Could you make a virtue out of this and construct a removable decking cover so that you have a usable space and then add planting around it? Just lift the decking for gas delivery access.