Mine is corroded. I think you're talking about where the hose goes into burner...correct?
Mines rusted closed, if it was ever operable...assuming we're talking about the same thing.
Got a lot of years out of that cheap burner, but its making my stainless brew pot ugly...and that pot ain't cheap.
Brewed a Hazy Pale, w/ Ekuanot.
Boiled 30 m's, because it was a hot day, & I was losing volume.
Gravity came in at 1.055 ish, w/ 5.5 gallons in the fermenter.
Recipe gravity was 1.047.
No sparge, single crush...pretty happy with that.
This what has worked for me:
Fermenter volume + 1 gallon for boil off + .125 gallons/lb of grain.
(Assuming a 60 minute boil).
Depending on how vigorous the boil is, can dictate how much volume you end up with.
Edit: I'm using BIAB, not eBIAB, for what its worth..