BuildCraft version: 7.99.8.2 (1.11.2)
Forge version: 1.11.2-13.20.1.2386
Multiplayer
Pipes do not connect with non-buildcraft stuff. (Forestry and Botania in my case)

if you're trying to connect kinesis pipes it won't work, BC uses MJ again

What types of pipe are you trying to connect to which blocks?

@iTitus I've tried to connect a Forestry engine and a Botania Mana Fluxfield. Both don't want to connect.
@AEnterprise Do you know a solution to that then?

BC uses MJ so directly connecting won't work, you'll need a power converter mod

also keep in mind the MJ mechanics are going to change completely soon