Blow Off On Conical Issue

[Ozhopper]

I have a conical fermenter. I have replaced the air lock with a blow off tube into a bottle with sterilised water.
When I take a sample from the side valve, it obviously draws out beer and creates a vacuum which raises water into the blow off tube from the bottle.
Usually when I have done this with a carboy and water has raised into the tube, I would raise the tube slightly out of the water and the water in the tube would drop back down into the bottle.
ISSUE: when I do this with a conical, the water keeps rising and ends up in my fermenter!!!
I cannot understand why this happens. Some thoughts have been that the tube is narrower than my previous blow off tubes. I have tried raising and lowering the bottle but no matter what position the water goes back into the fermenter.
Any ideas?

 

[caleb]

1. Remove the tube from the water when you take a sample.

OR

2. Put a one-way valve on the tube - air gets out, water can't get it.

 

[devo]

Have you tried temporarily removing the blow off tube from out of the water when taking a sample?

 

[Ozhopper]

1. Remove the tube from the water when you take a sample.

OR

2. Put a one-way valve on the tube - air gets out, water can't get it.

If I remove the tube then I risk oxidization. Not an issue when fermenting but when crash chilling to condition it could be.

Have considered a one way valve but will I be able to draw liquid if it will not allow fluid or oxygen up the blow off then the pressure will remain and the liquid won't flow out of the tap?

 

[barfridge]

You need to displace the liquid with something. If you're that paranoid about oxidisation, add a CO2 post at the top, so you can maintain a positive head pressure. Will solve your suction and oxidisation problems