Why would you want to empty the fire department's tanks immediately before you expect to need them full?
Which bit would they foam? The touchdown zone? The stop end? All the 3000m runway? The bit they reckon you'll stop on? The bit you reckon you'll stop on?
Sounds like a DC3/B17 procedure to me...dampen sparks when avgas is in the equation. Personally I'd prefer the tenders full and the foam directed where it is needed, when it is needed.