Underworld Connections: Tapping the Land for mana and ability?
No.

Tapping a land doesn't actually produce mana, activating its ability does. Tapping is merely the paying of the cost to do so.

Unlike abilities that read "Whenever enchanted land is tapped"[1], it's not actually tapping the land that causes Underworld Connections's effect. Tapping is merely paying part of the cost to do so.

As part of activating either the abilities, you will need to tap the land, which will leave you unable to activate the other ability.

Like in real life, just because two abilities have the same cost doesn't mean you can pay the price just once for both.




An example of such an ability is Utopia Sprawl's. Tapping the enchanted Forest for mana produces {G} as normal and triggers Utopia Sprawl's ability to produce a second mana.