There will be 2 lines, a send and a return, that run from your firewall under your 4runner to a small oval shaped hole up into your rear heater. You can cut these there and drain the coolant into something, then go back to your firewall and route the 2 hoses into each other using the T nipple already there. Then remove the heater from the inside of your runner.
Don't do it bro!!!! I love my rear heater. What's wrong with yours? Is it leaking, or is the fan not working? They're super easy to repair and maintain. And having that thing for camping is awesome, it totally heats up the back. Let me know if I can help you with this if you're on the fence about keeping it.
