other than through the Dungeon of the Crypt into Skullport, or through the portal in Xanathar’s hideout (again into skullport) are there other means of getting to the Underdark from the Waterdeep sewers? Through the Citadel of the Bloody Hand perhaps? There are. Long-forgotten tunnels from certain of the deepest dungeons of Castle Waterdeep, and there are two ways from the sewers to the caverns near Skullport, plus the Sea Caves and their shafts to Skullport, and thence to the Underdark. But NOT from the Citadel.#Realmslore

— Ed Greenwood (@TheEdVerse) February 24, 2019

So, to get from the sewers ti the Underdark, all ways lead through Skullport? i found the sewer map in FR1 ‘Waterdeep & the North’ can you point me to a supplement that would indicate where the sewers connect to the caverns near skullport? Some drow are looking to smuggle 1) No, not ALL ways lead through Skullport. All that can be used now, if found, without a lot of digging (due to collapses) lead through Skullport. And no, you've hit upon gaps in the published maps due to some projects never being pursued. So, no official supplements exist.

— Ed Greenwood (@TheEdVerse) February 24, 2019

2)
You'll have to {gasp) make it up. ;}

— Ed Greenwood (@TheEdVerse) February 24, 2019