If a foot lock drain plug isn't working properly, adjusting it may restore function to the plug. Adjustments can save time and money of replacements, and are relatively easy DIY projects.
Step 1 - Prepare the Plug
Put the plug in its open position. Run the hot water for several minutes to get rid of any soap scum that may have accumulated. Slippery residue can prevent tools from properly gripping the drain plug, and make repairs and adjustments difficult. Use a clean rag to dry inside of the drain plug. Close the plug and dry the outer surface.
Step 2 - Remove Clogs
Clogs of hair and other debris can prevent the drain from closing and opening properly, and slow the flow of water. Use channel locks to remove the top portion of the drain and access any clogs that may be present in the drain plug. Use channel locks to grab a hold of the large, upper portion of the drain.
Use another pair of channel locks or needle nose pliers to remove the knob. Underneath the top knob, you will find a screw or bolt that holds the drain assembly in place. Remove this portion of the drain plug assembly to access the bottom portion of the drain plug. Use the needle-nosed pliers to remove any hair or other debris that may have accumulated inside the drain plug.
Reassemble the drain plug by replacing the rod and the screw or bolt that holds it in place. Then replace the knob, and tighten the top portion of the assembly. Test the drain plug by opening and closing it, and running water, to see if that has fixed any issues you have been experiencing.
Step 3 - Look for Other Issues
If the drain still isn't functioning properly, check the rubber ring that surrounds the stem. It should rise and fall with the rest of the plug assembly when it is opened or closed. If the ring is stuck, it may not properly close. Try tightening the whole thing with the channel locks by twisting in a clockwise rotation. If that doesn't work, repeat the process to unscrew the assembly with the channel locks. The top portion of the plug is a relatively cheap part, usually coming in at less than fifteen bucks. Take the top part of the assembly to your local hardware store and purchase a replacement.
Step 4 - Replacing the Top of the Plug
Take the new plug and place it over the bottom of the assembly. Carefully set it so that the threading lines up. Screw clockwise until it is threaded, then use the channel locks to tighten. Close and open the drain to check for functionality. If the drain will not properly function or the drain plug is still not opening and closing, it's time to look at a complete assembly replacement.