Any FLAPS sells them.  It comes with several different size tees (to adapt
to different size heater hoses), a check-valve (to prevent flow back into
your garden hose--like that would ever happen) and a cap to close the tee
after you are done.  You leave the tee in place with the cap on it.  I
believe it comes with a couple of stainless hose clamps.  I use them on all
my vehicles.  It makes it much more likely I will change the coolant in a
timely manner.  I don't like pulling off hoses.   I'm sure the kit comes
with some instructions.   Pick a low spot underneath to cut in.  You are
cutting into a heater line--not the radiator lines!

                                                   Jay