most of them are located on the bottom of the tank mounted outside of the tank, with a little labor you should be able to do it, it will have 2 hoses and one plug ,you may have to remove a plastic guard protecting it, first see if you can buy one some aftermarket ones are cheaper than buying from dealer
most likely the over flow hose goes back there, when the car is over heating its bubbling out. First change the thermostat and then refill coolant and do a air bleed to the system. This is a very serious problem and I would not be driving this car for any length of time till problem is fixed. Pray its not the head gasket or that it has failed from over heating.
Has the system been flushed? Correct temperature thermostat installed? Are you getting flow through the radiator? Rad cap sealing properly and is it the correct one? Are the fans actually coming on? Is the temp sensor working properly? Rad properly filled or still have air trapped inside? Water level correct? Water pump working or seized, leaking?
