The Clay Fluid Pipe is a Fluid Pipe added by BuildCraft, that pushs any liquid, that travels through it, to the nearest Tank. If that tank is full the pipe will ignore that tank and pushs the liquid into the next available tank.
Different liquids will not mix together in the same pipe. However, if two different pumps are pulling out liquids and there is an empty pipe after one of the liquids passes through, the second liquid may be pumped into that empty pipe. When the two liquids reach a tank, the liquids will separate for each block of tank if there is space. If there is no extra space for the second liquid, it will backup and clog the piping system.