When i use electrical pump from Mekanism, i see how lava flows through the pipes (mechanical pipes from Mekanism too). Screenshots from creative mode where i reproduce this problem.

When i use pump from Buildraft & pipes from Mekanism - pipes visually remain empty (i tested this with any type of Mekanism pipes) but the transfer of liquid occurs.

Minecraft 1.7.10 + Buildcraft 6.0.17 + Mekanism 7.1.0.92.

Thanks!

This is just due to the BuildCraft pump releasing fluids very slowly - the pipes can transfer them faster than the visual updates.

Yep. If you only attach the pump end they fill up just fine.

About the last variant i wasn't thinking =) Thanks!