I have thought about adding a spigot to the kettle but it does not seem that it will solve the trub/hop sludge issues and only add cost.
Spigot is MUST have on brew kettle.
I have 10 gal kettle for 5 gal batches.
My kettle has about a gallon of dead space.
I start boiling with 8 gal and when I am done I have a little more then 6.5 gal.
Then chilling and whirlpooling.
After that let it sit in covered kettle for 30 min.
This is the time that all the hot break, hop matter and cold break settle to the bottom.
Then I drain kettle thru the spigot leaving all the trub in dead space ending up with 5.5 gal in fermenter.
Sorry for the lengthy answer.