how long

[chadrut72]

How long should I leave blow off tube in

 

[NordeastBrewer77]

until the krausen starts to drop back

 

[ATXweirdobrew]

Leave it in place until fermenatation is done and you plan to bottle.

 

[Stauffbier]

I don't use a blow off tube since I ferment in 7.5 gal buckets, but in your case I would probably remove it when krausen falls and then put an airlock on...