Abstract: A fluid detector comprises a probe, a probe cap and an electric cable connecting the probe and cap. A stainless steel lead is attached to the end of the probe opposite the cable. The distal end of an electrician's fish is inserted through an entry port into the space between the walls of a double-walled tank and run around the tank until it returns to the entry port. The end of the fish is engaged by a hook, pulled from the tank, and connected to the probe lead. The electric probe cable has a length equal to the distance from the entry port to the desired probe position. The fish lead and probe are pulled around the tank until the distal end of the fish emerges from the tank. The lead is disengaged from the fish and passed through the cap. The slack in the lead is taken in, and the lead is attached to the cap.

Abstract: A casing having rounded corners for ease of insertion into narrow confines defines a protective chamber and has openings permitting fluids exterior to the casing to enter the chamber. There is a fluid monitor within the chamber having a surface adapted for exposure to the fluids. There is a compartment within the casing insulated from the fluids and containing a second fluid monitor. A stainless steel cable is attached to the casing for inserting the probe between the walls of a double-walled tank. In an alternative embodiment there is a channel within the casing for receiving the distal end of an electrician's fish.