thanks a lot mr raghu
i guess i know my problems ....
1. i am trying to send the 5V signal over a length of 15mtrs .... i should be using 12V
2. I am using DC which will result in electrolysis of probes ... i should be alternating the flow of voltages between the sensor and the common plate.
3. Relay is not a good idea for switching as suggested by Mr. Steve ... so i should be using transistors ...

now my next set of problem ...
1. i will be able to alternate the flow using the P1 and some other pin to be connected to common plate. and i will be able to switch the 12V AC using BC547 kind of trasistor.... but in the end again ... when i need to sense the status of sensor (dipped or not) how do i read in the same port ...
am i supposed to connect a latch and a buffer to latch the values with one and read the values from the buffer where latch secondary and buffer primary are connected together to the sensor and the other sides of both connected to port pin ...

also am i supposed to be using CMOS buffer so that it can take 12V input and give 5V output

kindly help
nitin