I'm surprised this hasn't been fixed yet, but if you use the extractor with Shift+RMB on a blood container, it will take 1000 units of blood regardless of how much is actually there. For example, if the container has 130 units of blood, the extractor will still take 1000. This is an unbalanced duping issue.

Minecraft version: 1.7.10
Mod version: 0.9.13

Unfortunately, we don't support any version prior to 1.19.2 anymore. That is probably why it's not been fixed yet, and will not be.
We don't even track bugs here anymore prior to 1.8.

If the issue still persists in modern versions of the mod, feel free to create a new report for that, but I'll close this one for being out of support.